Influence of Repetitions-to-Failure Deadlift on Lumbo-Pelvic Coordination, With and Without Body Armor

Abstract

Ramirez, VJ, Bazrgari, B, Spencer, A, Gao, F, and Samaan, MA. Influence of repetitions-to-failure deadlift on lumbo-pelvic coordination, with and without body armor. J Strength Cond Res 38(10): 1732–1738, 2024—Repetition-to-failure (RTF) deadlift is a training modality for building lifting capacity that is often implemented by service members to maintain a minimum level of physical fitness. Despite its physiological benefits, little is known about the effects of RTF on the biomechanics of lumbar spine. Additionally, the effects of heavy deadlift training with body armor are unknown. The aim of this study was to investigate the effects of RTF deadlift on lumbo-pelvic coordination and posture, with and without body armor. Twenty-three healthy subjects, recreational powerlifters, were recruited for this study. Kinematics of the trunk and pelvis were measured using a 3D motion capture system while subjects conducted RTF deadlifts with a 68-kg low-handle hexagonal bar with and without a simulated body armor (22.68 kg). Lumbo-pelvic coordination was characterized using a vector coding approach and coupling angle variability (CAV) using circular statistics, over 3 equally divided segments of the lifting phase. More specifically, the coupling angle values were used to determine the coordination pattern between the thorax and pelvis. Trunk and pelvis ranges of motion and the amount of in-phase lumbo-pelvic coordination pattern increased with RTF deadlift. Additionally, CAV of the first and the third segments of deadlift cycle increased with RTF deadlift. Increase in variability of lumbo-pelvic coordination and peak trunk flexion (i.e., indication of increased mechanical demand of lifting on the spine), as a result of RTF deadlifting, can have deleterious soft tissue responses and contribute to an increase in risk of lower back injury.

Introduction

Low back pain (LBP) is a significant problem and one of the primary musculoskeletal conditions affecting active-duty service members (1). Low back pain affects training participation, deployment readiness, and results in increased medical costs (21). Idiopathic nature of most low back pain cases has forced preventive efforts toward risk factors management. In the military population, depending on the unit type within a Brigade Combat Team, the time spent wearing body armor and repetitive lifting have been identified as important risk factors for low back pain (22,31). Because these factors cannot be avoided or eliminated from combat missions, risk factor management cannot be implemented as an effective preventive strategy for combat missions. Hence, assuring that all soldiers maintain a minimum admissible level of fitness could be an alternative way of controlling or mitigating risk for lower back injuries and pain.

The Army Combat Fitness Test (ACFT) was developed to set a new minimum level of fitness for all soldiers to improve total Army fitness (Army Techniques Publication 7-22.01). The first event of the ACFT is the 3-repetition maximum (3RM) deadlift, which measures the overall strength and total lifting capacity of the soldier (35). However, LBP has been shown to be a common injury in the powerlifting population (6). To pass the 3RM deadlift, soldiers typically undergo certain types of training to improve their lifting capacity. One such training modality is repetitions-to-failure (RTF), or repetitive lifting to volitional failure (12,38). Failure here is defined as the muscle's inability to produce sufficient force to control the given load leading to termination of the exercise (38). Provided it is done to volitional failure, RTF has been shown to improve the overall strength and endurance of involved muscles while lifting high or low loads (2,12,13,25,34). Despite such physiological benefits, the biomechanical effects of such a physically demanding lifting-based training on the lower back (i.e., an important contributing factor in experience of low back pain) remain unknown.

The biomechanical changes in the lower back that occur when lifting to volitional failure have been demonstrated with lower loads (e.g., 13 kg) (29). Previous studies have found >20% increase in lumbosacral and trunk flexion when lifting to failure, which resulted in significant increases in passive bending moments at the lumbar spine (8,14). These alterations in posture place the lumbar spine in a kyphotic position during the lift and are associated with higher risk of injury to the lower back (4,5,19,20,27). Alterations in lower back biomechanics while performing RTF deadlift with heavy loads have yet to be investigated. Additionally, donning of body armor during RTF deadlift is encouraged because the deadlift component of the ACFT is used to simulate the movements while evacuating a casualty, which realistically is performed while wearing body armor (16). Therefore, it is not only important to investigate the changes in lower back biomechanics during RTF deadlift with heavy loads but also to determine the added impact of body armor if used to supplement such fitness training programs.

The aim of this study was to investigate how RTF deadlift, with and without body armor (BA), affects lumbo-pelvic coordination as a measure of lower back biomechanics. Based on previous studies of repetitive lifting of low weights, we hypothesized that RTF deadlift will cause increases in trunk and pelvic ranges of motion and alterations in lumbo-pelvic coordination involving more in-phase and less variable trunk motion relative to the pelvis. Additionally, it was postulated that such effects to be magnified in the presence of body armor. Given that a considerable number of musculoskeletal disorders in military are non–combat related (i.e., likely occurring during training) (24), a better understanding of changes in lower back biomechanics and the associated risk of low back injury with deadlift training could inform future mitigation strategies.

Methods

Experimental Approach to the Problem

A crossover study design was used to determine changes in lumbo-pelvic coordination from the initial to the final stage of RTF deadlift, with and without body armor. This completely within-subject repeated measures design allowed the comparison of the initial 10% and final 10% of total repetitions of RTF deadlift with and without body armor on lumbo-pelvic coordination and posture. The deadlift load was set at 68 kg and BA was simulated using a 22.68 kg weighted exercise vest (Air Flow Weighted Vest, MiR Vest Inc., San Jose, CA—Figure 1). The load of the deadlift was selected such to simulate a casualty weight according to an earlier study (16). The BA weight was evenly distributed between the front and back of the trunk. Data collection was performed over 2 days, 3–7 days apart to prevent the effects of fatigue, where the day in which the same subjects wore the BA was randomized.

Figure 1.

Starting (top row) and ending (bottom row) positions of a deadlift cycle with (right column) and without (left column) simulated body armor (vest).

An a priori power analysis was conducted for a repeated-measures, within factors, MANOVA, given an effect size f = 0.25, alpha (α) = 0.05, power = 0.80, number of groups = 4, number of measurements = 2, and correlation among measurements = 0.5, a sample size of 36 subjects was required. However, subject recruitment was halted because of Covid-19 laboratory closures in March 2020. Recruitment of subjects was conducted from July 2019 to March 2020. Twenty-eight subjects were recruited, from which because of marker occlusion and missing data points, only 23 subjects' datasets were used for data analysis.

Subjects

Twenty-three healthy adults participated in this study after obtaining written informed consent approved by the University of Kentucky Institutional Review Board (IRB# 48026). Subjects included 18 men and 5 women with mean ± SD age of 25 ± 5 years, height of 1.72 ± 0.07 m, and body mass 82.06 ± 16.44 kg. The inclusion criteria were experience with the deadlift exercise in the past year, a 3RM deadlift greater than 68 kg, a negative result on a Physical Activity Readiness Questionnaire (37), and no history of LBP or other musculoskeletal impairments or medical conditions that would prevent performance of the repetitive deadlift task.

Procedures

In the beginning, each subject performed self-selected stretches and a 5-minute warm-up on a cycle ergometer, at a self-selected pace and moderate resistance. After the warm-up, subjects were instrumented with 36 retro-reflective markers (9 mm in diameter) according to a Modified Cleveland Clinic market set (23). The trunk segment was identified with markers placed on C7, acromion (bilateral), and sternal notch, and the pelvis segment was defined with markers placed bilaterally at the anterior superior iliac spine, iliac crests, and posterior superior iliac spine. Subjects were then instructed to perform 3 to 5 familiarization deadlift repetitions during which they were reminded of proper deadlift form and other safety considerations. Foot placement was standardized by placing subjects' feet at shoulder width for all trials. The subjects were instructed to use the low-handle position on the hexagonal deadlift bar and perform the RTF deadlift using a “touch-and-go” lifting method at a self-selected pace and trunk inclination. Failure in the performance was identified when the bar was not in motion for longer than 2 seconds (stopping in the down or up position) or taking the hands off the bar. The subjects were allowed to let the weight touch the ground at the transition from lowering to lifting. No lifting straps, chalk, or belts were allowed. No feedback was given to the subjects on form/posture during the RTF deadlifts and only verbal encouragement was given to continue lifting to the best of their abilities. The number of repetitions completed were not disclosed to the subjects or shared with other subjects during or after testing to prevent bias during performance. During RTF deadlift, three-dimensional (3D) position of retroreflective markers was collected using a 15-camera motion capture system (Motion Analysis Corp., Rohnert Park, CA) at a rate of 100 frames per second.

Data Processing

Three-dimensional marker trajectory data were filtered with a fourth order, low-pass, Butterworth filter with a cut-off frequency of 6 Hz using Visual3D software (C-Motion, Inc., Germantown, MD) (39). Trunk and pelvis segment angles were defined with respect to the global coordinate system whereby the X-, Y-, and Z-directions represented the medial-lateral, anterior-posterior, and superior-inferior axes, respectively. Data processing was carried out on the first and last 10% of deadlift cycles representing the initial and the final stages of RTF deadlift. One deadlift cycle was defined from the maximum trunk flexion (i.e., starting position) to the maximum trunk extension (i.e., ending position) and did not include the lowering portion of the deadlift (Figure 2). Peak sagittal plane angular motions corresponding to pelvis anterior/posterior tilt (positive/negative sign, respectively) and trunk flexion/extension (positive/negative sign, respectively) were extracted for all deadlift cycles of the initial and the final stages of RTF deadlift.

Figure 2.

Trunk and pelvis angular motion for sample lowering and lifting cycles extracted from the initial and final stage of RTF deadlift of a subject. Lifting phase (right side of the curve) was used for coordination pattern identification and coupling angle variability measures. Each lifting phase (defined as lifting cycle in the text) was divided into 3 segments of equal trunk angular motion (denoted by circle markers) for these calculations. Positive/negative trunk angle denotes trunk flexion/extension; positive pelvic tilt denotes pelvic flexion. Circular markers are added for descriptive purpose and do not accurately represent the end point of first, second, and third segments of lifting cycle. RTF = repetitions-to-failure.

For the lumbo-pelvic coordination calculations, each deadlift cycle was divided into 3 equal segments based on the total trunk excursion during that cycle. These segments were labeled as the first, second, and third segments of the deadlift cycle. Lumbo-pelvic coordination was characterized using coupling angles between the trunk and pelvis (γ) (10,26) and circular statistics for coupling angle variability (3). Briefly, vector coding is implemented in this approach to quantify the spatial relationship between trunk and pelvic segments as coupling angles (10,26). The value of the coupling angles is then used to determine the lumbo-pelvic coordination patterns according to Needham et al. (26): in-phase (both segments move in the same direction), antiphase (both segments move in opposite directions), trunk-only motion (the trunk is moving whereas the pelvis does not), and pelvis-only motion (the pelvis is moving whereas the trunk does not), (Table 1). For each deadlift segment, the percent of data points in each of the 4 coordination pattern categories was calculated and then averaged across all the cycles of each RTF deadlift stage for subsequent analyses.

Table 1.

Scheme used to categorize coordination patterns.

Coordination pattern	Coupling angle (γ) ranges
In-phase	$22.5°\le \gamma \hspace{0.17em}<67.5°,202.5°\le \gamma \hspace{0.17em}<247.5°$
Pelvis only	$67.5°\le \gamma \hspace{0.17em}<112.5°,247.5°\le \gamma \hspace{0.17em}<292.5°$
Antiphase	$112.5°\le \gamma \hspace{0.17em}<157.5°,292.5°\le \gamma \hspace{0.17em}<337.5°$
Trunk only	$0°\le \gamma \hspace{0.17em}<22.5°,157.5°\le \gamma \hspace{0.17em}<202.5°,337.5°\le \gamma \le 360°$

Coupling angle variability (CAV) was calculated using circular statistics (3). Coupling angle variability is a measure of angular variance and equivalent to the standard deviation in linear statistics as seen in equation (1).

$${CAV}_i=\sqrt{2}\left(1-\overline{r_i}\right)\mid \frac{180}{\pi }$$ (1)

$$\overline{r_i}=\sqrt{{\overline{x_i}}^2+{\overline{y_i}}^2}$$ (2)

Where, $\overline{x}$ and $\overline{y}$, found in equation (2), are the average horizontal and vertical components of the coupling angle at each time point across all cycles of each RTF deadlift stage, and $\overline{r}$ is a measure of dispersion that ranges between 0 (no concentration about a single direction) and 1 (all points going in the same direction) (3). The average of CAV across all points for each deadlift segment was calculated to represent the CAV of that segment. A custom-written MATLAB (MathWorks, Natick, MA) script was used for all lumbo-pelvic coordination calculations.

Statistical Analyses

A paired t test was used to compare total repetitions performed with and without body armor. Descriptive statistics (mean and SD) were used for demographics and number of repetitions performed. A completely within subject, repeated-measures multivariate analysis of variance (MANOVA) was used to determine the changes in categories of coordination pattern and in CAV with the vest condition (with and without BA), task stage (the first and the final 10% of RTF cycles), and lifting segment (first, second, and third), as within-subject factors. A similar statistical analysis was used to determine changes in peak trunk and pelvis flexion/extension with the vest condition (with and without BA), and task stage (the first and the final 10% of RTF cycles), as within-subject factors. A Šidák correction was used to counteract the problem of multiple comparisons. The Huynh-Feldt correction was used for sphericity violation. A significance level of p ≤ 0.05 was used for all statistical tests and was supplemented by calculating effect size (ES) between variables, with ES > 0.5 representing moderate differences (36). All statistical procedures were performed using Statistical Package for the Social Sciences (SPSS) version 26 (IBM Corp., Armonk, NY).

Results

The total number of deadlift repetitions was greater for RTF deadlifts without versus with BA (p < 0.0001) with a mean ± SD total repetitions of 42 ± 17 versus 30 ± 16.

Posture

Peak trunk flexion (p = 0.0001; ES = 0.584), pelvic flexion (p = 0.003; ES = 0.346), and pelvic extension (p = 0.001; ES = 0.375) angles were all larger during the final versus the initial stage of the RTF deadlift (Figure 2). Subjects exhibited decreased peak trunk extension (p = 0.0001; ES = 0.462; Table 2) when performing the RTF deadlift with BA compared with the no BA condition.

Table 2.

Mean ± SD of peak flexion and extension angles of the trunk and pelvis during the initial and final 10% of the lift with and without the simulated body armor (BA).

	Trunk flexion		Pelvis flexion		Trunk extension		Pelvis extension
	Initial	Final	Initial	Final	Initial	Final	Initial	Final
No BA (deg)	−70.7 ± 12.4	−80.6* ± 16.9	−55.9 ± 8.1	−59.8* ± 9.7	−0.8 ± 4.7	−0.1 ± 4.9	−12.1 ± 5.5	−8.9* ± 6.1
BA (deg)	−72.6 ± 11.7	−80.5* ± 16.2	−56.4 ± 7.4	−58.1* ± 8.1	−3.9† ± 5.7	−1.9 ± 4.8	−11.0 ± 7.0	−6.8* ± 8.0

^*p < 0.05 between initial and final task stage

^†p < 0.05 between no BA and BA conditions.

Coordination Pattern

Lifting segment by task stage interactions were found in the amount (in percent) of in-phase (F(2, 21) = 20.291, p = 0.0001; Wilks' Λ = 0.341), antiphase (F(2, 21) = 14.694, p = 0.0001; Wilks' Λ = 0.417), and trunk-only (F(2, 21) = 8.201, p = 0.002; Wilks' Λ = 0.561) coordination patterns, such that each lifting segment was affected differently between the initial and final stages of the RTF deadlift. A vest by task stage interaction (F(1, 22) = 5.830, p = 0.025; Wilks' Λ = 0.791) and a vest by segment by task stage interaction (F(2, 21) = 3.921, p = 0.036; Wilks' Λ = 0.728) were found in the amount of antiphase coordination pattern such that the BA only affected the first and third segments of lifting segments and only during the initial stage of the RTF deadlift (Table 3).

Table 3.

Mean ± SD of trunk-pelvis coordination pattern over the 3 lift segments, with and without body armor (BA), by task stage (initial versus final).

	Segment 1		Segment 2		Segment 3
	Initial	Final	Initial	Final	Initial	Final
In-phase
No BA	53.6 ± 18.5	66.6 ± 17.0	89.7 ± 9.7	88.9 ± 15.9	61.2 ± 7.2	38.1 ± 31.0
BA	55.2 ± 16.6	68.6 ± 17.3	92.7 ± 6.9	91.2 ± 12.8	60.8 ± 37.9	39.4 ± 31.6
Antiphase
No BA	11.8 ± 7.8	6.3 ± 4.0	0.03 ± 0.17	0.22 ± 1.06	4.1 ± 10.2	7.6 ± 13.5
BA	8.8 ± 6.9	6.2 ± 5.5	0	0	1.1 ± 4.5	7.5 ± 11.8
Trunk only
No BA	26.7 ± 12.6	15.8 ± 9.9	10.3 ± 9.7	10.9 ± 16.0	33.4 ± 32.1	52.6 ± 27.7
BA	25.8 ± 14.1	16.6 ± 10.4	7.3 ± 6.9	8.8 ± 12.8	37.3 ± 37.3	49.1 ± 29.4
Pelvis only
No BA	7.9 ± 5.6	10.4 ± 7.5	0	0	1.4 ± 2.8	1.8 ± 3.7
BA	10.1 ± 7.7	8.8 ± 7.1	0	0	0.90 ± 2.7	4.0 ± 7.9

Coupling angle variability

Significant interaction was revealed in segment by task stage (F(2,20) = 8.738, p = 0.002; Wilks' Λ = 0.534) in CAV, such that only CAV of the first and the third segments of the deadlift cycle increased from the initial to the final stage of RTF deadlift (Table 4).

Table 4.

Means ± SD for coupling angle variability of the 3 lift segments, with and without a simulated body armor (BA), over the task stage (initial versus final).

	Segment 1		Segment 2		Segment 3
	Initial	Final	Initial	Final	Initial	Final
No BA (deg)	38.2 ± 16.3	41.3 ± 16.1	8.4 ± 1.1	8.5 ± 1.3	9.8 ± 4.9	12.2 ± 7.5
BA (deg)	42.0 ± 17.8	48.3 ± 13.8	8.6 ± 1.2	8.4 ± 0.9	8.9 ± 4.0	11.7 ± 8.2

Discussion

The purpose of this study was to investigate the effects of RTF deadlift on lumbo-pelvic coordination, with and without simulated BA. We hypothesized that RTF deadlift would result in increases in trunk and pelvis ranges of motion and alterations in lumbo-pelvic coordination involving more in-phase and less variable trunk motion relative to the pelvis. Additionally, we postulated that such effects would be magnified in the presence of BA. Consistent with our hypothesis, trunk and pelvis ranges of motion and the portion of in-phase lumbo-pelvic coordination pattern increased with RTF deadlift. The increase in the in-phase lumbo-pelvic coordination pattern, however, only occurred in the first segment of the deadlift cycle. Contrary to our hypothesis, CAV of the first and the third segments of deadlift cycle increased with RTF deadlift. The simulated BA condition only affected peak trunk extension where it decreased at the initial stage of RTF but resulted in no difference in the final stage.

Increases in trunk and lumbar flexion during repetitive lifting have been reported in previous studies (7,8,14,33), where a 13°–14° increase in peak trunk flexion was found with repetitive lifting of weights much lower than the deadlift weight used in our study (8,9). In our narrative review of repetitive lifting (29), we had postulated that repetitive lifting of heavy weights, compared with lower weights, would result in greater increases in trunk flexion angles. However, the current study demonstrated 10° and 4° RTF-induced increases in peak flexion angles of the trunk and pelvis, respectively, that are markedly smaller than those reported for repetitive lifting of lower weights. Contextually, the starting trunk flexion angle in studies of repetitive lifting of lower weights (7,8,14,33) ranged from 25 to 35°, whereas the starting trunk flexion angles in this study were 72.6 ± 11.7° and 70.7 ± 12.4° with and without BA, respectively. Starting the deadlift in such larger trunk flexed posture likely leaves minimal room for further increases in trunk peak flexion before the weight touch the ground. The restrictions imposed by the hex bar (e.g., requiring hands to be positioned outside of the knee as opposed to inside positioning of hand in repetitive lifting of lower loads) likely had some influences on the RTF-induced changes in trunk and pelvis posture exhibited in the present study.

For a nonfatiguing deadlift task, Zehr et al. (40) reported a dominantly in-phase (75% of time) lumbo-pelvic coordination, which is relatively consistent with our findings of lumbo-pelvic coordination during the initial stage of RTF deadlift. Specifically, during the initial stage of RTF deadlift, the portion of in-phase lumbo-pelvic coordination among our subjects was 53.6 ± 18.5%, 89.7 ± 9.7%, and 61.2 ± 7.2% for the first, second, and third segments of the deadlift, respectively. Although consistent with reported results by Zehr et al. (40), our results provide a more detailed picture of changes in lumbo-pelvic coordination as the lifter goes through different segment of lifting cycle. Hu and Ning (17) found a decrease in continuous relative phase between thorax and pelvis during a repetitive box lifting task, indicating a more in-phase lumbo-pelvic coordination. Similarly, our study found an increase in the in-phase coordination pattern with RTF deadlift, but only in the first segment of the lift cycle. Although phase angles and coupling angles cannot be directly compared, the directionality of the results are of interest for comparison with the results of this study. Further, our methodological approach enabled us to detect changes in lumbo-pelvic coordination that were not detected by earlier studies because of characterization of lumbo-pelvic coordination over the entire lifting phase (as opposed to over different lifting segments). Specifically, our results showed a decrease in in-phase lumbo-pelvic coordination with RTF deadlift in the third lift segment where a predominantly trunk-only pattern emerged (52%).

A decrease in variability of lumbo-pelvic coordination after repetitive lifting (17) and prolonged gait (32) tasks has been reported. However, an increase in lumbo-pelvic coordination variability with RTF deadlifts was found during the first and third segments of the deadlift cycle in this study and is indicative of reduced stability of trunk motion (or spine stability) during these specific segments of the deadlift. Such contradictory results are likely because of considerable differences in task investigated in the current study compared with those in earlier investigations. Specifically, the mechanical demand of the RTF deadlift task studied here on trunk muscles, compared with walking (32) and repetitive lifting of lower loads (17), was considerably larger. Nevertheless, the influence of methodological differences between this study and earlier investigations on reported results should not be overlooked.

There is limited information about the spinal loads experienced during a heavy deadlift (29). Cholewicki et al. (11) estimated that the spinal loads at the L4-L5, associated with 1 RM deadlift, can reach up to 8 and 18 kN in compressive forces, and 2 and 3.5 kN in anterior-posterior shear forces, for women and men, respectively. A recently published case report found spinal loads reaching over 17 and 4 kN in compression and shear force, respectively, while performing a 68 kg hex-bar deadlift using a dynamic musculoskeletal model (28). We are not aware of any report of changes in spinal loads with RTF deadlift; however, our finding of increases in trunk flexion with RTF deadlift suggest further increases in mechanical demand of deadlift with RTF. Considering the magnitude of spinal loads experienced during deadlift (11,28), further increases in spinal loads because of RTF-induced changes in trunk flexion will highly likely increase the risk of low back injuries.

There are a few limitations in this study that need to be acknowledged. First, because of the Covid-19 pandemic, we did not reach our desired sample size, which resulted in an underpowered study. Although it was underpowered, significance was reached by multiple variables. As with all fatiguing protocol studies, the duration of the effort put forth by the subjects (how many repetitions were performed under both conditions) is highly dependent on the subject's motivation to continue. Quantitative measures of fatigue, such as surface EMG or rate of perceived exertion, were not employed in this study and, hence, we cannot confirm that peripheral muscle fatigue of the erector spinae muscles occurred when performing the task. However, previous studies have demonstrated that erector spinae muscle fatigue does occur when employing a similar protocol (15,18,30). The subjects used in this study were healthy, generally fit, college students, a few ROTC cadets, and not active-duty service members. However, the mean age of the group, and ability to deadlift such weights, is similar to the active-duty soldier population; hence, the results can be useful when considering the applicability of this work to the soldier population. Marker placement on the skin introduces motion artifact especially when performing repetitive exercise, which causes perspiration and markers loosening. This was accounted for by ensuring markers were placed on dry skin before any perspiration occurred, which assisted in markers adhering to the skin without falling off.

Repetitions-to-failure deadlifting resulted in increased flexion of trunk and pelvis and alterations in lumbo-pelvic coordination that predominantly occurred in the first and third segments of the deadlift cycle. Such changes in biomechanics of lower back are associated with higher risk of injury because of increased mechanical demand of deadlift on the lower back (i.e., because of increases in trunk and pelvic flexion angles) and reduced stability of spine (i.e., reflected in increased variability of lumbo-pelvic coordination). Although the physiological benefits of RTF deadlift have been demonstrated (2,12,13,25,34), the associated risk for lower back injury should not be overlooked when preparing for physical readiness tests like the ACFT.

Practical Applications

The results of this study provide clinicians and practitioners a better understanding on which portion of the lifting phase of the deadlift is affected by repetitive lifting to volitional failure. We have identified the first and third portion of the lifting phase to be most affected, where the lift-off phase of the deadlift is also the point of greatest mechanical demand on the lower back. Although the physiological benefits of RTF deadlift have been demonstrated, this study shows there are associated risks for lower back injury that should not be overlooked. Practitioners should use caution when implementing an RTF deadlifting protocol in training programs.