Effects of Daytime Floatation-Restricted Environmental Stimulation Therapy on Nocturnal Cardiovascular Physiology, Sleep, and Subjective Recovery in Collegiate Student-Athletes: A Comprehensive Observational Study

Abstract

Vatne, E, Merrigan, JJ, Stone, JD, Saenz, C, Kraemer, WJ, and Hagen, JA. Effects of daytime floatation-restricted environmental stimulation therapy on nocturnal cardiovascular physiology, sleep, and subjective recovery in collegiate student-athletes: A comprehensive observational study. J Strength Cond Res 39(8): 857–867, 2025—The primary aim of this study was to explore the relationship between floatation-restricted environmental stimulation therapy (floatation-REST) and nocturnal cardiovascular physiology and sleep in collegiate athletes. The secondary aim was to describe the perceived changes in soreness, mood, fatigue, energy level, and overall experience after floatation-REST in collegiate athletes. Data included 214 records of nocturnal cardiovascular physiology and sleep collected using an acceptably valid and reliable wearable device (Ōura Ring, Ōura Health, Oulu, Finland) from 97 athletes (52.57% women) on 12 varsity teams, and 2,319 survey responses collected immediately after floatation-REST from 898 athletes (48.88% women) on 36 varsity teams. Nocturnal cardiovascular physiology was assessed through resting heart rate, heart rate variability, and respiration rate, while sleep was summarized using total sleep time, time in bed, and sleep efficiency. The representation of teams was varied, with football and men's and women's swimming heavily represented. Male and female athletes were analyzed separately to prevent overlooking sex-specific physiologic differences. Resting heart rate was significantly lower after floatation-REST than at night immediately before the session in female athletes (p < 0.001, effect size [ES] = −0.223) and male athletes (p < 0.001, ES = −0.186). Heart rate variability and sleep metrics showed no specific changes. In total, 98.7% of athletes reported an overall positive floatation-REST experience, and 85.3% felt better postsession, citing reduced soreness, stress, and fatigue, with improved energy. Thus, although more research is needed, these data provide a positive outlook for the use of this recovery technology in collegiate athletes.

Introduction

Recovery plays a pivotal role in the fitness-fatigue paradigm and thus sports performance because it directly influences an athlete's capabilities, training adaptations, and injury risk (15,32). One component of collegiate athletics relevant to their recovery is that student-athletes must balance a unique combination of time and energy commitments related to their training, competition, and academics (38). Appropriate recovery strategies can aid in managing collegiate student-athletes' physiologic, psychological, and mechanical stress (32). Although common recovery modalities (e.g., massage, cold-water immersion, and cryotherapy) tend to address postexercise soreness, fatigue, repair processes, and psychological stress (20), they are primarily used to support physiologic recovery. In contrast, floatation-restricted environmental stimulation therapy (floatation-REST) is a multidimensional recovery tool in which previous research reported positive impacts with respect to both physiologic and psychological recovery and well-being (9,10,13,19,44).

Floatation-REST places individuals in a quiet, warm, dark environment where they lie supine in skin-temperature, concentrated salt water, which reduces sensory input (visual, auditory, tactile, proprioceptive) to promote relaxation and recovery, which has been shown to have positive physiologic effects including cardiovascular and autonomic nervous system (9,10,13,19,44). One of the ways floatation-REST positively affects performance and recovery is by augmenting sports execution in precision-sport athletes (6,40,55) and reducing perceptions of fatigue and soreness in physically active individuals (9,10,13,19,44). More recently, floatation-REST was related to reduced soreness, improved mood, and reduced fatigue after an acute bout of exercise in physically active participants (13,44). Moreover, Caldwell and colleagues showed no blunting of the inflammatory and muscle damage response after resistance training in the floatation-REST condition compared with a passive recovery control (13). This finding is important because blunted inflammatory markers may explain the attenuated training adaptations, such as muscle hypertrophy, some have found from recovery modalities involving cold water or cryostimulation therapies (37).

A consequence of the stress student-athletes experience is inadequate sleep duration and poor sleep quality (39). Sleep has been established as an important factor for optimal performance and health among athletes (28). A recent systematic and meta-analytical review on the effects of acute sleep loss on physical performance found that, across the 69 publications reviewed, results indicate a significant negative impact of sleep loss on exercise performance in 7 different exercise categories: anaerobic power, speed/power endurance, high-intensity interval exercise, strength, endurance, strength endurance, and skill (17). Despite the compelling evidence for the importance of obtaining adequate sleep quantity and quality, collegiate athletes still fail to reach established sleep duration recommendations and report poor sleep quality (39). Floatation-REST may be one potential way for collegiate athletes to augment their sleep quality (1,21,34). Floatation-REST has demonstrated positive relationships with sleep quality through increased parasympathetic activity and promotion of relaxation in general and clinical populations (1,21,34). Broderick and colleagues demonstrated that, in team-sport male athletes, floatation-REST significantly improved perceived sleep quality compared with a passive recovery following a fatiguing exercise protocol (10). Therefore, research is warranted to investigate whether floatation-REST could be a method for improving sleep in this population.

The improvements in recovery after floatation-REST are proposed to be a result of nervous system modulation (1). Functional magnetic resonance imaging after floatation-REST revealed decreased patterns of resting-state functional connectivity in brain networks that are responsible for mapping our sense of self in healthy participants (1). These findings led authors to contend that floatation-REST potentially affects recovery through nervous system modulation, reducing self-reflective processes that are directed toward the current state of the body (1). The potential nervous system effects of floatation-REST from reduced sensory input and enhanced relaxation also result in anxiolytic benefits (21), improved mood (31), reduced stress (8,58), and enhanced feelings of well-being (33). More recently, Flux and colleagues investigated autonomic nervous system activity during floatation-REST sessions and concluded lower sympathetic arousal and balancing toward a more parasympathetic state (26). These potential benefits of floatation-REST could be especially valuable in collegiate athletes given the unique combination of physical and nonphysical stressors they experience.

Although the importance of recovery and benefits of floatation-REST for overall health and performance are well documented, it is essential to recognize the practical challenges that student-athletes face. Student-athletes often struggle to meet recommended sleep durations and report poor sleep quality (39). Furthermore, the demands of competitive sports compiled with rigorous academic schedules often leave student-athletes with insufficient time to fully leverage recovery strategies (38). Although there are many controlled studies showing improvements in subjective measures of wellness and sleep after the use of recovery strategies such as floatation-REST, there is limited objective data in the high-paced and high-pressure world of collegiate athletics. Subjective surveys have commonly been used to investigate the effects of recovery strategies, but these measures also have inherent limitations and biases, such as selection or expectancy bias (22). With the rapid improvements and increased access to athlete monitoring technologies, there becomes an opportunity to objectively evaluate the effectiveness of recovery modalities such as floatation-REST in applied sport environments. Notably, wearable devices such as sleep and nocturnal physiology monitors are now routinely out-performing previous nonpolysomnography wearable research devices such as actigraphy (14) and have more recently shown valid and reliable physiologic recovery measures of sleep, resting heart rate, and heart rate variability (43,54). Wearable devices with acceptable levels of validity and reliability used within athlete monitoring paradigms present an innovative way to investigate the relationships between recovery strategies and physiologic markers while being sensitive to the congested schedules of collegiate athletes.

Although previous investigations have demonstrated improvements in subjective measures of perceived sleep quality, soreness, and fatigue after floatation-REST, there remains a lack of objective data collected from applied, dynamic, and high-pressure environments such as collegiate athletics. The lack of empirical evidence describing effects of recovery strategies on athletes leaves practitioners, support staff, and athletes themselves choosing recovery strategies based on “rule-of-thumb” heuristics as opposed to scientific literature (29). To begin addressing this opportunity, this study aims to leverage routine athlete monitoring processes that use wearable devices with proven acceptable levels of accuracy and reliability to explore the relationship between a daytime floatation-REST session and changes in sleep and nocturnal cardiovascular physiology in student-athletes. The study team hypothesized that improvements in sleep quantity (time asleep, efficiency) and sleep physiology (resting heart rate reduction, heart rate variability increases) would be seen acutely after a floatation-REST session. Furthermore, this study also investigates subjective feedback collected immediately after floatation-REST sessions to explore acute, postsession effects. Thus, this study serves as an important starting point for the exploration of postsession effects of recovery strategies in elite athletes.

Methods

Experimental Approach to the Problem

This retrospective, observational cohort study included data from standard operations and procedures between 2018 and 2023 within the university's athletic department to examine changes in sleep and nocturnal cardiovascular parameters after floatation-REST and to analyze subjective immediate postsession feedback describing floatation-REST experience Division I (DI) athletes. Student-athletes completed a 60-minute, daytime floatation-REST session in 1 of 4 permanently installed tanks (Superior Float Tanks; Quest Float Suite Standard, 94″ × 52″ × 88″ L × W × H) as their recovery demands and their individual schedules permitted. Each floatation-REST tank environment includes 94.5° ± 0.5° Fahrenheit concentrated Epsom salt water maintained at 1.25–1.275 specific gravity (measured by digital hydrometer). Water is kept sanitized through a 1 μm filtration, ozone, and ultraviolet light treatment that cycles 3 complete times after each session is completed. Each athlete is educated on the procedures in-person by a staff member, which includes showering before and after the session, given the option to have limited light and relaxing sounds played, and the session duration of 60 minutes. If the athletes self-reported a session duration of <60 minutes, the data were excluded from analysis. Immediately after the floatation-REST session, student-athletes completed a standardized survey regarding their experience and changes in perceived soreness, fatigue, and stress. This internally developed survey presented student-athletes with the opportunity to select positive and negative responses to questions about their feelings before, during, and after the floatation-REST session and describing the overall experience. Data were subsequently analyzed as counts and frequencies of the feelings selected for each question. The survey also included 1 open-ended question to provide student-athletes with the opportunity to provide comments about the session. The survey responses were collected through tablet located directly outside of the floatation-REST tank and stored in the department's athlete management system (Smartabase, Teamworks). Eight hundred ninety-six student-athletes across 36 varsity teams completed a daytime floatation-REST session and immediately completed the postsession survey. Athlete experience with floatation-REST as a recovery modality varied with first time session (29.7%), one previous session (16.9%), 2 to 3 sessions (19.3%), and more than 3 sessions (37.1%). Floatation-REST sessions that were completed specifically to treat an injury or concussion were excluded from this study and only floatation-REST sessions completed for general recovery from collegiate athletics stressors were included.

Based on device availability, athletes were also provided with and properly sized for a wearable device (Ōura Ring Generation 2, Ōura Health, Oulu, Finland) to measure sleep and nocturnal cardiovascular physiology as a part of routine athlete monitoring procedures. The variables analyzed in this study from the wearable device were resting heart rate, heart rate variability, respiration rate, total sleep time, time in bed, and sleep efficiency. The Ōura Ring has been shown to be a valid and reliable device for the 2-stage categorization of sleep versus wake and for cardiovascular measurements such as resting heart rate and heart rate variability (14,43,53,54). To be included in this analysis, student-athletes must have worn their wearable device during the 7 nights preceding the day of the floatation-REST session and the night immediately after the session. Any student-athletes with less than the 8 required sleep and nocturnal cardiovascular physiology records around the floatation-REST session were excluded. Two hundred fourteen records from 97 student-athletes across 13 varsity teams met the inclusion criteria for the analysis of sleep and nocturnal cardiovascular physiology data surrounding a floatation-REST session. The data collected from the wearable device were automatically sent to and stored in the same athlete management system as the survey responses and deidentified before statistical analysis. Data from Oura were assessed for validity and outlier detection by analyzing 5-minute epoch data from heart rate for each night, and rejecting any records that contained >5% missing data, because this could be due to improper fit or wear.

Subjects

In compliance with standard procedures within the athletic department, participants completed the postsession survey after every floatation-REST session and regularly wore their wearable device during sleep if they were provided with one. The Ohio State University Institutional Review Board (Protocol #2022H0036) approved the retrospective analysis of deidentified data collected as a part of standard procedures of the athletic department. The analysis of sleep and nocturnal cardiovascular physiology data before and after the floatation-REST session included a total of 214 records from 97 NCAA Division I athletes (52.57% women, details in Table 1) on 12 different varsity sports. To be included in this analysis, the student-athlete must have volunteered to complete a floatation-REST session and worn his or her wearable device each of the 7 nights preceding the floatation-REST session and the night immediately after the session. Student-athletes with 1 or more nights missing were omitted from the analysis. The CONSORT diagram in Figure 1 outlines how the final sample of sleep records was achieved.

Table 1.

Team sample sizes and age.^*

	Postsession survey analysis		Wearable analysis
	n	Age	n	Age
Sport
Women's basketball	16		3
Women's diving	9		1
Field hockey	34		8
Women's ice hockey	34		10
Women's soccer	39		8
Women's swimming	55		20
Women's track and field	11		1
Men's diving	7		2
Football	114		5
Men's ice hockey	41		4
Men's swimming	54		26
Men's volleyball	21		7
Wrestling	19		2
Women's cheer	9
Dance	11
Women's fencing	15
Women's golf	8
Women's gymnastics	22
Women's lacrosse	34
Novice rowing	2
Women's pistol	1
Rowing	53
Softball	31
Synchro. Swimming	22
Women's tennis	11
Women's volleyball	22
Baseball	54
Men's basketball	14
Men's cheer	23
Men's fencing	9
Men's golf	13
Men's gymnastics	20
Men's lacrosse	45
Men's pistol	1
Men's soccer	19
Men's track and field	5
Total	898	20.19 ± 2.71*	97	20.06 ± 3.29*
Total female athletes	439	19.85 ± 2.97	51	19.63 ± 4.04
Total male athletes	459	20.53 ± 2.38	46	20.68 ± 1.50

^*Data are presented as mean ± SD.

Figure 1.

Consort flow diagram for nighttime sleep and recovery data.

Data from the survey completed after the floatation-REST session for recovery included at total of 2,319 sessions from 898 NCAA Division I athletes (48.88% women, details in Table 1) across 36 varsity teams. Although all athletes have access to floatation-REST and the survey, not all athletes have an Oura ring based on accessibility of the devices, which can be seen from 898 athletes with survey data and 97 with Oura data. Only floatation-REST sessions completed for general recovery from collegiate athletics stressors were included. The CONSORT diagram in Figure 2 outlines how survey responses were filtered to achieve the final sample. The mean start time of the floatation-REST sessions was 1:03 pm (±2 hours and 37 minutes). The distribution of athletes across the 13 varsity sports included in the sleep and cardiovascular physiology analysis and the distribution of athletes across the 36 varsity teams included in the postsession analysis was varied. The number of athletes from each sport included in the analyses is presented in Table 1.

Figure 2.

Consort flow diagram for postsession survey data.

Procedures

Sleep and Nocturnal Cardiovascular Physiology

Athletes were properly fitted for and provided with a second-generation Ōura Ring (Ōura Health, Oulu, Finland) and were instructed to wear the ring every night. Rings were monitored by staff of the department of athletics to maintain data quality. Retrospectively, records were filtered to only include student-athletes’ records that included all 7 nights before and the night immediately after the floatation-REST session. The ring uses photoplethysmography (PPG) sensors for collecting pulse wave-based heart rate measurements and uses a proprietary algorithm (3) to combine cardiorespiratory data from its PPG sensors, body temperature data from its negative temperature coefficient sensor, and movement data from its 3-dimensional accelerometer to estimate sleep parameters. The Ōura Ring is acceptable for field measures of cardiovascular recovery parameters, such as resting heart rate (RHR) and pulse rate variability, which is presented as heart rate variability (HRV) compared with electrocardiography, and for the 2-stage (sleep and wake) classification of sleep compared with polysomnography and electroencephalography (43,53). The metrics used from the Ōura Ring for the present investigation were RHR, HRV, respiration rate (RR), total sleep time, time in bed, and sleep efficiency as reported by the Ōura application. Resting heart rate is the student-athlete's average heart rate across the 5-minute epochs during sleep, presented in beats per minute. The HRV index reported by the Ōura Ring is the root mean square of successive differences (rMSSD) in milliseconds. Root mean square of successive differences represents vagally derived, parasympathetic modulation of cardiac activity, and is used in athlete monitoring as an indicator of recovery and autonomic balance and, collectively, RHR and HRV are used to assess physiologic state in athlete monitoring literature (11,47–49,52). Similar to RHR, HRV is reported as an average of the 5-minute epochs throughout the night. Total sleep time is the number of hours that the student-athlete spends in light, deep, and REM sleep stages. Time in bed is the total number of hours that the student-athlete was in bed both awake and asleep. Sleep efficiency is the ratio of total sleep time divided by the total time in bed presented as a percentage with a maximum value of 100.

Subjective Postfloat Response Survey

The internally developed postsession survey used in this study was developed to assess fatigue, stress, soreness, and energy level before and after the floatation-REST session (Table 4). The survey also gauged overall experience during the floatation-REST session by presenting student-athletes with the opportunity to select as few or as many positive and negative responses to questions about their feelings before, during, and after the floatation-REST session and describing the overall experience. The athletes completed the survey through tablet located directly outside of the floatation-REST tank immediately on cessation of the session. The survey included 7 total questions with an option to provide additional comments about the session. The questions about the student-athletes’ feelings before, during, and after the floatation-REST session and describing the overall experience were analyzed by calculating frequencies of the responses that were selected for each question and frequencies of the responses. The contextual survey questions collected information about the reason for the session (general recovery, injury, or concussion) and how many floatation-REST sessions the student-athlete has done before.

Table 4.

Seven-day Z-scores of sleep and nocturnal cardiovascular physiology.^*

Sex	Variable	Mean 7-day Z-score ±SD	Test statistic	p
Female athletes
	RHR 7-day Z-score	−0.23 ± 0.86	2,830.00	<0.001 †
	HRV 7-day Z-score	0.03 ± 0.93	4,130.00	0.377
	RR 7-day Z-score	−0.06 ± 0.95	3,597.00	0.326
	TST 7-day Z-score	−0.13 ± 0.87	3,292.00	0.095
	SE 7-day Z-score	0.02 ± 0.87	4,180.50	0.662
	TiB 7-day Z-score	−0.17 ± 0.86	3,198.00	0.037
Male athletes
	RHR 7-day Z-score	−0.03 ± 0.91	1,731.00	0.220
	HRV 7-day Z-score	0.12 ± 1.04	2,185.00	0.126
	RR 7-day Z-score	0.05 ± 0.86	1,861.00	0.885
	TST 7-day Z-score	−0.01 ± 0.91	1,847.00	0.946
	SE 7-day Z-score	0.15 ± 0.91	1,988.00	0.186
	TiB 7-day Z-score	−0.08 ± 0.93	1,705.00	0.378

^*RHR = resting heart rate; bpm = beats per minute; HRV = heart rate variability; rMSSD = root mean square of successive differences; RR = respiration rate; rpm = respirations per minute; TST = total sleep time; SE = sleep efficiency; TiB = time in bed.

^†Statistically significant difference between 7-day Z-Score and 0 (SD).

There are inherent biases and limitations associated with the use of subjective surveys. For example, athletes may exhibit a tendency to report more positive experiences to appease researchers or staff within the department of athletics. To mitigate these biases, the survey was designed with questions that include positive, negative, and neutral responses and athletes were encouraged to provide genuine and honest feedback. Despite these considerations, it remains critical to interpret the results of this survey while recognizing the potential impact of social and expectancy biases.

Statistical Analyses

Data are reported as mean ± SD. Data were assessed for normality with Shapiro–Wilk testing and were found to significantly deviate from normal distribution for all variables of interest. Owing to the lack of normal distributions and extreme values that could skew parametric tests, nonparametric analyses that are more robust against violations of assumptions were used. Paired-samples Wilcoxon Signed-Rank tests were conducted to identify differences between the night immediately before and the 7-day average before the floatation-REST session compared with the night immediately after the session for the sleep and nocturnal cardiovascular physiology metrics. In addition, Wilcoxon effect sizes (27) were calculated to present standardized mean differences between the time points. Because of the inconsistent evidence of effects of menstrual cycle phase on heart rate parameters (4,5,7,36,41,50,56), nocturnal averages for male and female athletes were analyzed separately. However, data were not available to account for the effect of menstrual cycle on sleep and nocturnal cardiovascular physiology parameters in this study. In addition, 1-sample Wilcoxon-Signed Rank tests were applied to assess whether sleep and nocturnal cardiovascular physiology z-scores were significantly different from 0. The z-scores were calculated using previous 7-day rolling averages and standard deviations along with the value for the night after the floatation-REST session. Z-scores are commonly used within sport science to understand how an individual athlete's measurement deviates from their average value, which is particularly important to control for individual variations in measures such as RHR and HRV (46,59). Subjective postsession survey results were coded to calculate sums and frequencies of feedback responses and chi-square tests were used to assess statistical differences of athletes' responses to the survey questions. An alpha of 0.8% (p < 0.008) was used to determine statistical significance to control for multiple comparisons. All statistical analyses and visualizations were conducted using R, version 4.2.1 (R Core Team, Vienna, Austria; https://www.R-project.org).

Results

Statistically significant changes in acute nocturnal cardiovascular physiology markers were observed after the floatation-REST session in male and female athletes. RHR was significantly decreased after the floatation-REST session compared with the night before the session in both male (p < 0.001, Wilcoxon effect size [ES] = −0.186) and female athletes (p < 0.001, ES = −0.223) (Table 2 and Figure 3). In the comparisons between the night after the floatation-REST session and the 7-night average leading up to the day of the floatation-REST session, which allowed for a normalized rolling average comparison, RHR (p < 0.001, ES = −0.367) was significantly decreased after floatation-REST in female athletes. There was a statistically insignificant yet small effect size for a decrease in RHR (p = 0.017, ES = −0.227) and increase in HRV (p = 0.032, ES = 0.198) after the floatation-REST session compared with the previous 7 nights in male athletes (Table 3 and Figure 4). Means, standard deviations, and effect sizes for sleep and nocturnal cardiovascular physiology are presented in Tables 2 and 3. The average RHR 7-day Z-Score was statistically significantly different from 0 according to the Wilcoxon-Signed Rank test (p = 0.003) in female athletes (Table 4).

Table 2.

Prefloat vs. postfloat sleep and nocturnal cardiovascular physiology.^*‡†

Sex	Variable	Prefloat mean ± SD	Postfloat mean ± SD	p	Effect size
Female athletes
	RHR (bpm)	54.53 ± 6.73	53.93 ± 6.65	<0.001 ‡	−0.223
	HRV (rMSSD; ms)	98.93 ± 39.7	100.65 ± 37.49	0.201	0.074
	RR (rpm)	15.51 ± 1.43	15.5 ± 1.45	0.701	0.032
	TST (hours)	7.2 ± 1.1	7.16 ± 1.05	0.937	−0.007
	SE (%)	85.83 ± 6.5	86.02 ± 6.15	0.982	0.009
	TiB (hours)	8.39 ± 1.19	8.32 ± 1.07	0.992	−0.001
Male athletes
	RHR (bpm)	53.54 ± 6.88	52.94 ± 6.97	<0.001 ‡	−0.186
	HRV (rMSSD; ms)	79.99 ± 39.69	82.84 ± 41.66	0.079	0.143
	RR (rpm)	15.28 ± 1.66	15.15 ± 1.6	0.024	−0.252
	TST (hours)	6.33 ± 1.06	6.49 ± 1.25	0.294	0.108
	SE (%)	79.66 ± 7.12	79.66 ± 8.16	0.529	0.068
	TiB (hours)	7.96 ± 1.21	8.14 ± 1.43	0.516	0.069

^*RHR = resting heart rate; bpm = beats per minute; HRV = heart rate variability; rMSSD = root mean square of successive differences; RR = respiration rate; rpm = respirations per minute; TST = total sleep time; SE = sleep efficiency; TiB = time in bed.

^†p-value for significance in this case is 0.05 divided by 6 for multiple comparisons, or 0.0083.

^‡Statistically significant difference between prefloat and postfloat values.

Figure 3.

Floatation-REST effect on nocturnal cardiovascular physiology and sleep prefloat vs. postfloat.

Table 3.

Prefloat 7-day average versus postfloat sleep and nocturnal cardiovascular physiology.^*†

Sex	Variable	Prefloat mean ± SD	Postfloat mean ± SD	p	Effect size
Female athletes
	RHR (bpm)	54.75 ± 6.29	53.93 ± 6.65	<0.001 ‡	−0.367
	HRV (rMSSD; ms)	99.07 ± 31.26	100.65 ± 37.49	0.113	0.108
	RR (rpm)	15.53 ± 1.37	15.5 ± 1.45	0.240	0.104
	TST (hours)	7.26 ± 0.63	7.16 ± 1.05	0.280	−0.096
	SE (%)	85.87 ± 4.6	86.02 ± 6.15	0.669	0.039
	TiB (hours)	8.46 ± 0.65	8.32 ± 1.07	0.160	−0.125
Male athletes
	RHR (bpm)	53.37 ± 6.22	52.94 ± 6.97	0.017	−0.227
	HRV (rMSSD; ms)	79.48 ± 33.73	82.84 ± 41.66	0.032	0.198
	RR (rpm)	15.16 ± 1.51	15.15 ± 1.6	0.290	0.113
	TST (hours)	6.42 ± 0.75	6.49 ± 1.25	0.719	0.037
	SE (%)	79.29 ± 5.89	79.29 ± 8.16	0.067	0.197
	TiB (hours)	8.11 ± 0.8	8.14 ± 1.43	0.727	0.038

^*RHR = resting heart rate; bpm = beats per minute; HRV = heart rate variability; rMSSD = root mean square of successive differences; RR = respiration rate; rpm = respirations per minute; TST = total sleep time; SE = sleep efficiency; TiB = time in bed.

^†p-value for significance in this case is 0.05 divided by 6 for multiple comparisons, or 0.0083.

^‡Statistically significant difference between prefloat and postfloat values.

Figure 4.

Floatation-REST effect on nocturnal cardiovascular physiology and sleep 7-day average prefloat vs. postfloat.

Subjective Postsession Survey

The findings of this study support the initial hypothesis that the subjective questionnaire responses would reflect an overall positive experience of the floatation-REST session among collegiate athletes and would reflect subjective improvements in fatigue, soreness, stress, and energy level after the floatation-REST sessions. Results of the chi-square analysis demonstrate that the frequencies of the responses are statistically significantly different for each postsession survey question. In total, 98.6% (2,288) of the 2,319 postsession survey responses indicated an overall good experience. When asked about feeling better, worse, or the same after the session, 85.3% (1977) of athletes reported feeling better, 5.7 and 0.08% reported feeling the same or worse after the session, respectively, while 9% chose to skip this question. Furthermore, survey results demonstrated that most student-athletes felt relaxed, mentally at ease, and fell asleep during the floatation-REST session. After floatation-REST, 60.6% of student-athletes reported feeling more rested and 40.4% reported feeling less stressed. Student-athletes’ feedback also reflected feeling less fatigued and sore with improvements in energy level after the floatation-REST session. Sums and frequencies of the responses to the survey questions are presented in Table 5 and Figure 5.

Table 5.

Counts and frequencies of postsession survey responses.^*

Survey question	Survey response options	Count	Frequency	Χ2	p
How was the overall float experience? (select one)	Good	2,288	98.7%	2,196.66	<0.001*
	Bad	31	1.3%
How did you feel during the float session (select all that apply)	Fell asleep	1,519	65.5%	3,451.25	<0.001*
	Mind was at ease	1,340	57.8%
	Mind was racing	255	11%
	Felt bored	233	10%
	Relaxed	1934	83.4%
	Uncomfortable	124	5.3%
How did you feel after the float session (select all that apply)	Better	1977	85.3%	1,657.58	<0.001*
	Worse	2	0.1%
	Same	132	5.7%
	No selection	208	9%
What changes did you notice after the float session? (select all that apply)	Reduced soreness	733	31.6%	4,527.44	<0.001*
	Reduced stress	936	40.4%
	Reduced fatigue	860	37.1%
	Improved energy	402	17.3%
	More rested	1,405	60.6%
	Feel foggy	249	10.7%
	Feel sluggish	189	8.2%
Total responses		2,319

^*Statistically significant result for Chi-Square analysis.

Figure 5.

Subjective feedback from during and after Floatation-REST.

Discussion

This study identified acute improvements in nocturnal cardiovascular physiology after a single, daytime floatation-REST session in elite student-athletes. Furthermore, subjective responses collected immediately after the completion of floatation-REST sessions reflected largely positive perceived changes and overall experience. Statistically significant improvements in RHR were observed the night after a floatation-REST session compared with the night before for both male and female athletes. In male athletes, there were statistically insignificant yet small effect sizes identified for a decrease in nocturnal average RHR and increase in nocturnal average HRV after the floatation-REST session compared with the previous 7-day average. When comparing the previous 7-night average with the values of the night after the floatation-REST session in female athletes, only a statistically significant reduction of RHR was observed. Survey responses collected immediately after the floatation-REST session demonstrated that most (98.7%) of the 2,319 survey responses from student-athletes reported a positive overall experience during the session, and the responses also reflected subjective, perceived improvements in fatigue, soreness, energy level, and mood. Furthermore, most survey responses reflected that student-athletes felt better (85.3%) after the floatation-REST session as opposed to worse (0.1%) or the same (5.7%). Although the hypothesis of coupled improvements in nocturnal average RHR and HRV after floatation-REST in both male and female athletes was not confirmed, the findings of this study serve to continue to increase the understanding of how floatation-REST affects global recovery in elite collegiate student-athletes.

Coupled trends of RHR and HRV are commonly used in athlete monitoring literature as cardiac-autonomic markers of recovery and used to understand physiologic states (11,47–49,52). In this study, male and female athletes exhibited small effect sizes for a decrease in RHR after the daytime floatation-REST session compared with (1) the night immediately before and (2) the previous 7-day average, and a significant increase in HRV compared with (2) the previous 7-day average. These changes may be reflective of a shift toward a more parasympathetic state and improved global recovery (11,48,52). Simultaneous improvements in RHR and HRV correlate with improved perceptions in well-being and physical performance in elite athletes (48,52). In a case study of an elite collegiate cross-country athlete, weekly mean, mean RHR, and HRV were moderately correlated with 8-km race times (23). In another group of endurance runners, percentage change in HRV was highly correlated with variation in 5-km performance and race performance time (18). Thus, improvements in RHR and HRV reflected by the small effect sizes in this study may have enhanced athletes' ability to perform, but more research is warranted to test this hypothesis.

Changes in nocturnal cardiovascular physiology before and after the floatation-REST session were analyzed separately for male and female athletes. In this study, HRV was significantly greater across all time points in female athletes than in male athletes, which is consistent with the literature identifying relative dominance of vagal, parasympathetic activity in female athletes' autonomic control (35). In addition, only RHR showed a significant difference after the floatation-REST session in female student-athletes. Nocturnal average heart rate parameters may be complicated by the effects of hormone phases of the menstrual cycle or the use of hormonal contraceptives in female athletes (4,5,7,36,41,50). For example, in a sample of NCAA Division I rowers, HRV measurements collected 3 times per week across an 18-week season demonstrated a significantly reduced average HRV (LnRMSSD) during the weeks that menses was recorded even when controlling for training load (50). Alzueta and colleagues reported lower nocturnal average rMSSD HRV during the luteal phase in a cohort of healthy women with regular, ovulatory cycles (4). Other research has also reported decreased time-domain (e.g., SDNN or rMSSD) HRV measurements at rest in eumenorrheic women in the luteal phase compared with the follicular phase (5,36,41,56). These observations are potentially attributable to effects of estrogen on cardiovascular physiology, such as increased blood volume and vasoconstriction (42). However, the methods of the studies investigating the effects of menstrual cycle phase on HRV varied widely. Heart rate variability measurements across the menstrual cycle have been collected using photoplethysmography (4,50) and electrocardiography (41,56). Nonetheless, the lack of significant differences in HRV in female athletes of the present study could be the result of nocturnal monitoring without accounting for the context of a female athlete's menstrual cycle phase and contraceptive use, which was not available for this study. It is plausible that menstrual cycle phase was a confounding factor affecting HRV in this investigation, but further research describing the effects of menstrual cycle on athlete monitoring approaches and metrics in athletes is warranted.

The wearable device used in this study only reports rMSSD, a time-domain HRV feature that reflects parasympathetic activity and vagal tone (2). Consistent with previous findings, rMSSD did not show significant changes after floatation-REST in this study (26). However, there are other HRV features that may be worth exploring after floatation-REST. Flux et al. (26) reported that although rMSSD was not significantly different, a frequency-domain HRV feature, normalized low frequency (nLF), showed a decrease during floatation-REST (26). Because nLF is associated with sympathetic nervous system activity, its reduction is suggested to indicate a decrease in sympathetic nervous system activation (12). Although frequency-domain HRV features are not reported by the wearable device used in this study, it is possible that certain aspects of autonomic nervous system activity were overlooked by only reporting 1 HRV feature, and a broader range HRV analyses should be used in future studies to better understand the influence of floatation-REST on autonomic nervous system activity. This could be explored with access to time series data (i.e., interbeat interval) during sleep as opposed to a single summary metric available in the consumer platform.

Additional potential causes for limited changes and small effect sizes for the acute effects of floatation-REST on nocturnal physiology may be because of the lack of control and context about training load demands the student-athletes were experiencing at the time of their floatation-REST. HRV has been shown to be associated with training demands, and even by sport position and body mass (25). Because this was an observational study, and did not control for training load, nutrition, or academic demands, potential confounders may exist that account for the lack of more significant findings in nocturnal cardiovascular physiology. Furthermore, research has demonstrated elevated and more stable HRV compared with age-matched, nonathlete comparisons (23,24,51). A lack of significant improvement in HRV after floatation-REST could be attributable to the already high and stable HRV values of highly trained athletes. Future work could include investigating whether athletes with lower and less stable HRV values demonstrate significant improvements in HRV after floatation-REST compared with the athletes who already have higher HRV values, or what other factors characterize responders and nonresponders to floatation-REST. In addition, modeling considerations that account for variations at the athlete level (e.g., linear mixed models) may assist in furthering the understanding of individual responses to flotation-REST in high-performance populations.

Contrary to prior research describing the relationship between floatation-REST and subjective improvements in sleep, there was no significant difference in objective sleep metrics before and after the daytime floatation-REST session in the present investigation (8,10,31,34,45). However, a limitation of this study was no subjective information was collected that describes sleep in this cohort of student-athletes surrounding their floatation-REST session. Previous investigations of the effects of floatation-REST on sleep reported improvements in subjective perceptions of sleep quality and quantity (8,10,31,34,45). A recent review by Kjellgren et al. found that floatation-REST demonstrated a beneficial effect on sleep that was maintained at 4- and 6-month follow-ups in clinical and nonclinical studies (34). One study found a significantly greater improvement in perceived sleep quality after floatation-REST compared with a passive recovery control condition in a group of male, team-sport athletes (10). Similarly, in a group of adults with stress-related ailments, floatation-REST was associated with significant improvements in perceived sleep quality (8). The perceptions of improved sleep in previous studies could be attributed to increased parasympathetic modulation and anxiolytic effects from floatation-REST (1,8,21). No objective changes in sleep quantity were observed after floatation-REST in this study, which may be because of athletic and educational demands on the overall timing and amount of sleep (i.e., early classes or training sessions, late study sessions, or competitions).

The subjective effects of floatation-REST on perceptions of mood, energy, soreness, and fatigue in this work are the first at this large-scale reported, to our knowledge, in NCAA Division I collegiate athletes, and are consistent with previous research in other populations, such as recreationally active, healthy adults (6,9,10,13,19,44). While studying a group of 19 male, team-sport athletes, Broderick and colleagues demonstrated that the reduction in perceived muscle soreness and physical fatigue was significantly greater for floatation-REST than for the control condition of sitting in a dim-lit room (10). Similar findings were reported by Driller and Argus in 60 elite, male and female, international-level athletes across 9 sports (19). In this study, athletes completed a floatation-REST session after an exercise training session and collected answers from a validated, multidimensional mood-state questionnaire before and after the floatation-REST session. A single, floatation-REST session significantly improved 15 of the 16 mood-state variables that were collected and also significantly decreased muscle soreness (19). Although this study used an internal questionnaire to collect responses immediately after the floatation-REST session, the subjective responses to floatation-REST were consistent with observations collected with validated surveys in other studies. In the interest of being sensitive to student-athletes’ time and maximizing compliance, the survey was developed to minimize the time requirements and collect as much broad contextual information as possible in the limited number of questions. Although this was not a clinically validated survey instrument, our findings demonstrated the utility of an efficiently designed survey to maximize the opportunity to collect large scale data in a high-paced sport environment, which allows for both acute and longitudinal scientific investigations. Even validated surveys, however, include inherent limitations and biases. For example, athletes may respond a particular way to a survey question to please the researcher or out of concern that their coach may be able to see the responses. Therefore, although this study presents overwhelmingly positive empirical evidence of positive acute effects of floatation-REST, the data should be interpreted appropriately given the context and methods used for collection.

Collegiate student-athletes are required to balance full schedules related to their athletics, academic, and personal commitments (38). Because of cumulative time constraints experienced by student-athletes that place supreme value on resource allocation, engagement in effective and time-efficient recovery modalities is crucial to habitual and worthwhile utilization. For these reasons, studies similar to this one that present high degrees of ecological validity are necessary to continue the depth of knowledge in fields of study, such as the role of floatation-REST, in athletic populations. Despite the high ecological validity of this experimental design, there are opportunities future investigations to improve the methods of applied investigations like this study. For example, the objective sleep and nocturnal cardiovascular data could be presented with additional context beyond the floatation-REST session (e.g., competition and academic demands). Furthermore, in this study, data describing any confounding effects of female athletes' menstrual cycle on nocturnal cardiovascular physiology were unavailable. To minimize the effects of menstrual-phase–related variations in heart rate metrics affecting the statistical analyses in this study, male and female athletes were analyzed separately. Assuredly, it is pertinent to continue to research how to best use heart rate metrics in female athletes. To date, monitoring studies tend to focus on male athletes or fail to address menstrual cycle considerations because female athletes have been underrepresented in sport science and sports medicine research (16,30). Emerging research highlights the practical considerations to best adapt traditional athlete monitoring models to female athletes (57) and the value of this information to optimize training adaptations and performance (16). Still, novel athlete monitoring approaches that are sensitive to female athlete physiology have not been widely explored, including not yet in collegiate athletics. Future directions should include how to analyze female athlete-specific markers in wearable-focused research in practical and applied manners. Including a control condition could also help understand whether the changes in nocturnal cardiovascular physiology are more directly attributable to the floatation-REST session. Finally, accounting for experience with floatation-REST in the analysis may provide insights into long-term impacts on athletes' performance and recovery. Overall, this retrospective study describes the effects of floatation-REST within a real-world environment of student-athletes. The acute effects of floatation-REST on nocturnal cardiovascular physiology and subjective well-being in student-athletes suggest that the findings of previous investigations of floatation-REST in different populations may extend to collegiate athletes.

In summary, this study demonstrated that a daytime floatation-REST session was associated with improvements in nocturnal cardiovascular physiology and subjective perceptions of wellness and recovery in elite collegiate student-athletes. Coupled significant improvements in HRV and RHR were observed in male athletes while significant reductions in RHR were observed in female athletes after a single, daytime floatation-REST session. Furthermore, in 2,319 records of surveys collected immediately after floatation-REST sessions for recovery, the results demonstrated largely positive experiences and improvements in stress, soreness, fatigue, restfulness, and energy. The positive effects that were reported in this investigation suggest that floatation-REST may be a beneficial and ecologically valid approach to promote recovery in collegiate student-athletes in their real-world environments.

Practical Applications

The present investigation has demonstrated that a single, daytime floatation-REST session is related to improvements in elements of nocturnal cardiovascular physiology and subjective perceptions of recovery and wellness in elite collegiate athletes. Historically, practitioners have prescribed recovery modalities to athletes based on best practices and heuristics. The findings of this study, while they are presented with limited external validity for the sake of heightened ecological validity, greatly add to the understanding of the acute effects of floatation-REST in collegiate athletes. During times of high stress from training, competition, or academic demands, floatation-REST may be a potentially valuable recovery strategy to improve nocturnal cardiovascular metrics of recovery and acute, subjective perceptions of fatigue in athletes. In addition to physical benefits, floatation-REST may also positively contribute to mental health and overall well-being. Furthermore, taking into consideration individual athlete needs and preferences could allow for more targeted, prescriptive recovery. Overall, the combination of athlete monitoring technology capable of identifying periods of autonomic imbalance with recovery modalities such as floatation-REST, which promotes parasympathetic activity, could manage the effects cumulative stressors, help reach states of relaxation, and improve general recovery in collegiate athletes.