Abstract
Background:
Among young athletes returning to sport after anterior cruciate ligament reconstruction (ACLR), the extent to which psychological readiness is influenced by factors beyond the psychological domain is largely unknown.
Hypothesis:
Young athletes with recent sport exposure and higher quadriceps strength will demonstrate higher psychological readiness within 8 weeks of medical clearance to return to sport (RTS) after ACLR.
Study Design:
Cross-sectional study.
Level of Evidence:
Level 3.
Methods:
A total of 38 young athletes after primary ACLR completed testing within 8 weeks of medical clearance to RTS. All participants completed isometric knee extension strength testing, in addition to the ACL Return to Sport after Injury (ACL-RSI) questionnaire. Athletes who participated in sport between time of medical clearance to RTS and date of study enrollment were categorized as SPORT-YES. Those who had not yet participated in sports were categorized as SPORT-NO. Multiple linear regression analyses were used to determine differences in ACL-RSI scores based on quadriceps strength and sport exposure status, while adjusting for age and sex.
Results:
Of the 38 participants, 20 (52.6%) were categorized as SPORT-YES. The regression model estimating overall ACL-RSI score (P < 0.01, adjusted R2 = 0.389) included significant independent contributions from age, sex, and sport exposure variables (age: P = 0.01, β [95% CI] = -2.01 [-3.54, -0.48]; sex (male): P = 0.02, β [95% CI] = 12.50 [2.36, 22.64]; strength: P = 0.51, β [95% CI] = -2.47 [-10.07,5.13]; sport exposure: P < 0.01, β [95% CI] = 12.89 [3.58, 22.19]).
Conclusion:
In partial accordance with our hypothesis, recent sport exposure was significantly associated with higher ACL-RSI scores among young athletes in the weeks after medical clearance to RTS after ACLR, while quadriceps strength was not.
Clinical Relevance:
Future prospective work is needed to determine the existence and direction of causal relationships between exposure to sport environment and psychological readiness among young athletes after ACLR.
Keywords: anterior cruciate ligament, psychological readiness, quadriceps strength, sport participation
Incidence of anterior cruciate ligament (ACL) injuries in adolescent athletes has continued to rise in recent years. 5 It is estimated that athletes aged 15 to 25 years make up 50% of the total ACL injuries reported annually, indicating that this population is at an elevated risk.6,15 Yet, many young athletes who suffer an ACL injury and undergo ACL reconstruction (ACLR) demonstrate difficulty in returning to their previous level of sport within 12 months of surgery. 30 This is concerning, as returning to sport participation is often the primary goal among this population. 30
There is recent evidence to support psychological readiness as a significant contributor to successful rehabilitation and return to previous level of competition after ACLR.1-4,17,22,28 Higher psychological readiness has been associated with a higher rate of return to sport (RTS), faster RTS, and a greater likelihood of returning to previous participation level. 2 Several factors have been identified to influence psychological readiness, including fear of reinjury, poor function, lack of trust in area of injury, and fear of repeating the rehabilitation process.2,26,28 However, there is limited evidence on the extent to which psychological readiness is influenced by factors beyond the psychological domain, such as physical strength and exposure to the sport environment.
Little is known about the impact of quadriceps strength on psychological readiness after ACLR. Often considered a key factor in physical readiness to RTS after ACLR, the attainment of sufficient quadriceps strength has been found to influence RTS rate, risk of reinjury, knee joint health, and patient-reported function.11,20 Lepley et al 19 reported a positive correlation between isometric quadriceps strength and psychological readiness after ACLR. Yet, contrary evidence also exists, indicating no relationship between measures of quadriceps function and psychological readiness to RTS.13,24 In addition, to our knowledge, no other studies have investigated the impact of sport exposure on psychological readiness at time of clearance to RTS after ACLR. It is important to recognize that the COVID-19 pandemic uniquely limited or fully restricted sports participation for many adolescent athletes. Pandemic-related loss of sports participation among healthy youth has been associated with higher anxiety and lower quality of life, both of which likely impact psychological readiness to RTS after injury. 21 Furthermore, inconsistencies across rehabilitation protocols result in varying amounts of allowed sport exposure before clearance to unrestricted sport participation after ACLR. 14
Therefore, the purpose of this study was to determine whether psychological readiness is associated with quadriceps strength and sport exposure. First, we hypothesized that young athletes who demonstrated higher quadriceps strength in the weeks after clearance to RTS would also demonstrate higher psychological readiness. Second, we hypothesized that young athletes who were exposed to preinjury level of sport during this time would demonstrate higher psychological readiness.
Methods
Participants
This study included a cohort of 38 participants from an ongoing longitudinal study of outcomes after primary ACLR among young athletes. Participants were included if they met the following criteria: (1) 13 to 25 years of age; (2) had undergone primary, unilateral ACLR; (3) had been cleared to RTS by provider (physician/physical therapist) within the previous 8 weeks; and (4) planned to return to a pivoting/cutting sport for at least 50 hours per year. The participants were excluded if they sustained a concomitant ligament injury (except for Grade I medial collateral ligament injury); required concomitant surgical procedure (except for meniscal debridement or repair); had a history of lower extremity (aside from current ACL injury) or spine injury requiring surgery or continued medical care; or underwent a pediatric, physeal-sparing ACLR. The study team did not control rehabilitation nor RTS decision-making for this study. This study was approved by the internal Institutional Review Boards at Cincinnati Children’s Hospital Medical Center and The Ohio State Wexner Medical Center. Written formal consent and/or parental permission were obtained before testing.
Data Collection
Participants were enrolled within 8 weeks of medical clearance for unrestricted sports participation by their physician or physical therapist. At a baseline laboratory visit (RTS visit), participants completed the Anterior Cruciate Ligament Return to Sport after Injury (ACL-RSI) questionnaire, isometric knee extension strength testing, and a sport participation survey. Participants were enrolled in this study between January 1, 2020 and December 31, 2021, after the onset of the COVID-19 pandemic.
Psychological Readiness
All participants completed the ACL-RSI questionnaire to assess psychological readiness to RTS participation. The ACL-RSI is a 12-item questionnaire scaled 0 to 100, with higher scores indicating higher psychological readiness. 29 The ACL-RSI can be divided into 3 subscales that measure key domains of psychological readiness, including Emotions, Confidence, and Risk Appraisal. The ACL-RSI is a valid and reliable measure of psychological readiness for those returning to sport after ACLR. 29 ACL-RSI overall scores and subscale scores were used for analysis.
Quadriceps Strength
The participants underwent an isometric quadriceps femoris strength testing protocol using an isokinetic dynamometer (Biodex Medical Systems Inc). Participants were secured in a seated position of 90° of hip flexion and 60° of knee flexion. To measure the maximum volitional isometric contraction of the quadriceps femoris, the participants were asked to perform a 5-second, maximal effort, isometric knee extension movement with their arms crossed against their chest in the testing position. Participants were instructed to “kick out as hard as you can for 5 seconds” and were given a 10-second rest between trials. Starting with the uninvolved lower extremity, 3 trials were performed on each side. Peak torque (in Newton-meters [N.m]) across 3 trials of isometric knee extension was recorded and normalized by body weight (N.m/kg). Limb symmetry index (LSI; [involved limb quadriceps peak torque/uninvolved limb quadriceps peak torque]) was calculated for each participant.
Sports Exposure
Participants completed a sport participation survey at the RTS visit which asked, “Have you returned to the same level of sports as before your injury?” Participants who responded “yes” to this question were categorized as Sport Exposure-Yes (SPORT EXP-YES). Those who had not yet returned to preinjury level of sports participation and answered “no” were categorized as Sport Exposure-No (SPORT EXP-NO). If a participant was categorized as SPORT EXP-NO, a self-reported reason for not returning to preinjury level of sport was recorded. Participants were also asked to report how many preinjury-level sports practices and games they had participated in since medical clearance to RTS. Practice and game exposures were recorded for participants in both groups, though intensity level of each exposure (eg, preinjury level vs lower than preinjury level) was not recorded.
Statistical Analysis
Descriptive statistics were used to calculate demographic data of the entire cohort. Multiple linear regression analyses were used to determine difference in ACL-RSI scores based on isometric quadriceps strength and sport exposure status, while adjusting for age and sex. These analyses were replicated using isometric quadriceps strength LSI as the independent variable for strength. Multicollinearity of independent variables was assessed through inspection of correlation coefficients and tolerance/variance inflation factor values <0.1. 16 To detect differences in demographic, psychological readiness, and strength data between SPORT EXP-YES and SPORT EXP-NO groups, independent samples t tests and chi-square analyses were used for continuous and categorical data, respectively. Independent samples t tests and chi-square analyses were also used to determine differences in demographics, psychological readiness, and strength among participants in the SPORT EXP-NO group, based on reason for not participating in preinjury-level games or practices. Effect sizes were calculated for mean differences between groups. All statistical analyses were performed using SPSS software (Version 25; IBM Corp).
A sample size of 35 participants was deemed sufficient to detect an effect size of 0.40 (f2) with 0.80 power and an alpha level of 0.05 for a multivariable regression model with 4 predictor variables (isometric quadriceps strength, sport exposure, age, and sex) (G*Power, Version 3.1). A total of 38 participants were used for this analysis to accommodate for unexpected issues with data collection and analysis.
Results
A total of 38 young athletes were enrolled in this study within 8 weeks of medical clearance to RTS after primary ACLR. Descriptive statistics for demographic data are presented in Table 1. Mean age of participants in the SPORT EXP-YES group was significantly lower than that of participants in the SPORT EXP-NO group (16.8 ± 2.3 years vs 19.1 ± 3.6 years; P = 0.03).
Table 1.
Cohort demographics presented by group
| Characteristic | SPORT EXP-YES (n = 20) | SPORT EXP-NO (n = 18) | P value | Effect Size (Cohen’s d) |
|---|---|---|---|---|
| Age, y | 16.80 ± 2.33 | 19.08 ± 3.59 | 0.03 * | 0.76 |
| Sex | ||||
| Female | 15 (39.5%) | 12 (31.6%) | 0.57 | |
| Male | 5 (13.2%) | 6 (15.8%) | ||
| Height, cm | 168.81 ± 9.58 | 169.99 ± 7.70 | 0.68 | 0.14 |
| Weight, kg | 67.27 ± 15.19 | 73.93 ± 18.75 | 0.24 | 0.39 |
| Time between ACLR and RTS, mo | 10.14 ± 2.11 | 9.38 ± 1.20 | 0.19 | 0.44 |
| Time between medical clearance and RTS visit, days | 23.60 ± 11.61 | 25.39 ± 19.40 | 0.73 | 0.11 |
| Preinjury Tegner Activity Scale score a | 9 (7-10) | 9 (7-10) | 0.72 | |
| Graft type | ||||
| Hamstring tendon autograft | 11 (28.9%) | 11 (28.9%) | 0.52 | |
| Patellar tendon autograft | 4 (10.5%) | 5 (13.2%) | ||
| Quadriceps tendon autograft | 5 (13.2%) | 2 (5.3%) |
ACLR, anterior cruciate ligament reconstruction; RTS, return to sport.
Statistically significant value.
Reported as median (range); Tegner Activity Scale score is a measure of activity level on a 0 to 10 scale, with a score of 0 indicating “on sick leave/disability” and a score of 10 as “participation in competitive sports such as soccer at a national or international elite level.” Activity levels 6 to 10 represent participation in recreational or competitive sports. 27
Of the 38 participants in this study, 20 (52.6%) were categorized as SPORT EXP-YES, and 18 (47.4%) were categorized as SPORT-EXP NO (Figure 1); 11 participants from 1 institution were categorized as SPORT EXP-YES, while 9 participants from the second institution were categorized as SPORT EXP-YES. The mean physical therapy visit count for each site was 49.2 ± 9.7 (n = 24) and 42.2 ± 4.4 (n = 14), respectively. Self-reported reasons for not returning to preinjury level of sport among the SPORT EXP-NO group are reported in Figure 1. The SPORT EXP-YES group reported 372 total sport exposures since medical clearance to RTS (304 practices, 68 games). The SPORT EXP-NO group reported 85 total sport exposures (77 practices, 8 games). Number of practice and game exposures reported by each participant are reported in Figure 2. The regression model was significantly associated with ACL-RSI overall score (F[4,33] = 7.06, P < 0.01, adj. R2 = 0.40), ACL-RSI Emotions subscale score (F[4,33] = 7.81, P < 0.01, adjusted [adj.] R2 = 0.42), and ACL-RSI Confidence subscale score (F[4,33] = 5.19, P < 0.01, adj. R2 = 0.31), while adjusting for age and sex (Table 2). Sport exposure explained 7.2% to 19.4% of the total variance in these scores (semipartial correlation coefficients: ACL-RSI overall score = 0.36 [P < 0.01], ACL-RSI Emotions = 0.27 [P = 0.04], ACL-RSI Confidence = 0.44 [P < 0.01]). Age and sex were associated with ACL-RSI overall score and ACL-RSI Emotions subscale score, when adjusting for strength and sport exposure. Younger age and male sex were associated with higher ACL-RSI scores. The regression model was not associated significantly with ACL-RSI Risk Appraisal subscale score (P = 0.08). Similar results were found in the analyses using isometric quadriceps strength LSI as the independent variable for strength (Appendix 1, available in the online version of this article). In these analyses, sport exposure was no longer a significant independent contributor to the overall model estimating ACL-RSI Emotions subscale score (P = 0.06, β [95% CI] = 11.00 [-0.24, 22.25]). Lack of multicollinearity was confirmed, as all correlation coefficients were <0.7 (range, -0.54 to 0.50) and tolerance values were >0.1 (range, 0.82 to 0.88). Isometric quadriceps strength was not associated independently with any measure of psychological readiness. ACL-RSI scores and strength data are presented by group in Table 3. A secondary analysis revealed no differences in demographic, ACL-RSI scores, or strength data for those in the SPORT EXP-NO group who reported their sport was not in season (n = 11) compared with those with other reasons for not participating in preinjury-level games or practices (n = 7) (Table 4).
Figure 1.
Categorization of participants based on exposure to preinjury level of sport. Self-reported reasons for not returning to preinjury level of sport listed on left for SPORT EXP-NO group. Participants intended to return to the following sports after ACLR: soccer (13/38; 34.2%), basketball (10/38; 26.3%), baseball/softball (4/38; 10.5%), lacrosse (3/38; 7.9%), volleyball (2/38; 5.3%), gymnastics/tumbling (2/38; 5.3%), football (2/38; 5.3%), ultimate Frisbee (1/38; 2.6%), dance (1/38; 2.6%). ACLR, anterior cruciate ligament reconstruction.
Figure 2.
Practice, game, and total sport exposures reported by each participant, categorized by (a) SPORT EXP-YES and (b) SPORT EXP-NO. Participants in each group are represented by integers on x-axis.
Table 2.
Results of multiple regression analyses
| Age | Sex | Quadriceps Strength | Sport Exposure | |||
|---|---|---|---|---|---|---|
| Adj. R2 | P value of Model | β (95% CI) | β (95% CI) | β (95% CI) | β (95% CI) | |
| ACL-RSI Overall score | 0.396 | <0.01 | −2.01 (−3.54, −0.48)* |
12.50 (2.36, 22.64)* |
−2.47 (−10.07, 5.13) |
12.89 (3.58, 22.19)* |
| ACL-RSI Emotions score | 0.424 | <0.01 | −3.16 (−4.99, −1.32)* |
16.38 (4.23, 28.52)* |
−1.82 (−10.93, 7.28) |
11.81 (0.67, 23.96)* |
| ACL-RSI Confidence score | 0.312 | <0.01 | −1.118 (−2.71, 0.47) |
9.27 (−1.25, 19.79) |
−3.15 (−11.04, 4.74) |
15.37 (5.71, 25.03)* |
| ACL-RSI Risk Appraisal score | 0.117 | 0.09 | −1.36 (−3.37, 0.65) |
10.88 (−2.46,2 4.21) |
−2.41 (−12.40, 7.59) |
9.38 (−2.86, 21.62) |
ACL, anterior cruciate ligament; ACL-RSI, ACL Return to Sport after Injury questionnaire; Adj. R2, adjusted coefficient of determination; β, unstandardized regression coefficient.
Statistically significant value.
Table 3.
Psychological readiness and strength data presented by group
| SPORT EXP-YES | SPORT EXP-NO | P value | Effect size (Cohen’s d) | |
|---|---|---|---|---|
| ACL-RSI overall score | 87.83 ± 11.46 | 71.34 ± 17.76 | <0.01* | 1.12 |
| Emotions subscale score | 81.80 ± 17.57 | 64.11 ± 20.11 | <0.01* | 0.94 |
| Confidence subscale score | 94.90 ± 6.37 | 77.67 ± 19.22 | <0.01* | 1.23 |
| Risk Appraisal subscale score | 85.25 ± 15.52 | 73.61 ± 19.54 | 0.05* | 0.66 |
| Involved limb isometric quadriceps strength, peak torque, N.m/kg | 2.64 ± 0.66 | 2.67 ± 0.60 | 0.88 | 0.05 |
| Uninvolved limb isometric quadriceps strength, peak torque, N.m/kg | 2.89 ± 0.66 | 2.81 ± 0.71 | 0.73 | 0.11 |
| Isometric quadriceps strength LSI, % | 92.6 ± 16.8 | 96.2 ± 12.6 | 0.46 | 0.24 |
ACL, anterior cruciate ligament; ACL-RSI, ACL Return to Sport after Injury questionnaire; LSI, limb symmetry index.
Statistically significant value.
Table 4.
Comparison of participants in SPORT EXP-NO group
| SPORT EXP-NO, Sport Was Not in Season (n = 11) a | SPORT EXP-NO, Other (n = 7) | P value | Effect Size (Cohen’s d) | |
|---|---|---|---|---|
| Age, y | 18.54 ± 3.49 | 19.92 ± 3.87 | 0.45 | 0.38 |
| Sex | ||||
| Female | 8 (66.7%) | 4 (33.3%) | 0.49 | |
| Male | 3 (50.0%) | 3 (50.0%) | ||
| Height, cm | 171.03 ± 6.97 | 168.34 ± 9.04 | 0.49 | 0.34 |
| Weight, kg | 72.92 ± 18.37 | 75.51 ± 20.71 | 0.79 | 0.13 |
| Time between ACLR and RTS, mo | 9.24 ± 1.19 | 9.59 ± 1.28 | 0.56 | 0.29 |
| ACL-RSI overall score | 74.39 ± 15.36 | 66.55 ± 21.37 | 0.38 | 0.44 |
| Emotions subscale score | 66.36 ± 20.24 | 60.57 ± 20.97 | 0.57 | 0.28 |
| Confidence subscale score | 83.45 ± 13.36 | 68.57 ± 24.32 | 0.11 | 0.82 |
| Risk Appraisal subscale score | 71.82 ± 18.20 | 76.43 ± 22.69 | 0.64 | 0.23 |
| Involved limb isometric quadriceps strength, peak torque, N.m/kg | 2.60 ± 0.58 | 2.78 ± 0.67 | 0.55 | 0.30 |
| Uninvolved limb isometric quadriceps strength, peak torque, N.m/kg | 2.83 ± 0.74 | 2.78 ± 0.71 | 0.89 | 0.07 |
| Isometric quadriceps strength LSI, % | 92.9 ± 9.4 | 101.5 ± 15.8 | 0.17 | 0.70 |
ACL, anterior cruciate ligament; ACLR, anterior cruciate ligament reconstruction; ACL-RSI, ACL Return to Sport after Injury questionnaire; LSI, limb symmetry index; RTS, return to sport.
“Sport was not in season” was the reason chosen by 11 participants when asked why they had not yet participated in preinjury-level games or practices. The remaining 7 participants reported reasons including “muscle weakness,” “timing did not work out,” “parent is worried,” and “fear of reinjury.”
Discussion
The purpose of this study was to evaluate the association between quadriceps strength and sport exposure, and psychological readiness among adolescents returning to sport after ACLR. In partial accordance with our hypothesis, exposure to preinjury level of sport was associated with higher psychological readiness at the RTS visit. However, no association was found between quadriceps strength and psychological readiness among this population. Among the participants who had not yet been exposed to preinjury level of sport at the time of the RTS visit, over half reported their sport not being in season. Further, despite level of sport exposure, the SPORT EXP-YES group reported participation in over 400% more sport exposures than the SPORT EXP-NO group. The findings of this study serve as an important lens for the unique needs of young athletes approaching RTS after ACLR.
Effect of Sport Exposure
Interestingly, participants who reported exposure to preinjury level of sport after RTS clearance after ACLR demonstrated mean ACL-RSI scores estimated to be approximately 11 to 16 points higher than those without the same level of sport exposure. There is evidence to indicate that more frequent sport participation before an ACL injury is associated positively with higher psychological readiness at time of RTS after ACLR. 30 What is still unknown is how sport exposure during the weeks after RTS influences psychological response. The findings from the current study indicate that exposure to sport practices or games during this time may positively influence psychological readiness. Yet, future research is required to identify the existence and direction of a causal relationship between sport exposure and psychological readiness, as it is also possible that higher psychological readiness may influence RTS timing.
Implementation of sport-specific or on-field interventions during late-stage rehabilitation has been shown to improve psychological readiness to RTS.8-10 As such, reintegration to the sport environment during the rehabilitation process may be an important intervention for successful achievement of psychological readiness among young athletes, warranting future research. These results may also indicate that, if sport exposure is a critical part of psychological readiness for athletes after ACLR, reconsideration of the timing of psychological readiness assessment may be warranted.
Effect of Quadriceps Strength
While past work has studied various physical and psychological factors that may hinder a young athlete’s readiness to return to preinjury level of sport after ACLR, quadriceps strength is often considered to be a primary contributing factor to RTS success.1-4,11,17,20,22,28 After ACLR, greater quadriceps strength at the time of RTS has been associated with greater knee joint function and higher psychological readiness. 19 Yet, the results of the current study indicate that greater isometric quadriceps strength may not be associated with more positive scores for self-reported psychological readiness. Interestingly, O’Conner et al 24 also found no significant differences in isokinetic quadriceps strength between athletes with high ACL-RSI scores compared with athletes with low ACL-RSI scores at 9 months after ACLR. Yet, in contrast to these findings, Della Villa et al 12 reported a positive relationship between quadriceps LSI and psychological readiness among athletes after ACLR. The aforementioned studies studied cohorts with varying demographics and utilized diverse methods for quadriceps strength assessment. More recent studies have examined the relationship between psychological readiness and alternative measures quadriceps performance, such as single-leg hop testing, yet no significant relationships have been reported.13,24 While conflicting evidence on the association between quadriceps strength and psychological readiness at time of RTS after ACLR continues to exist, our results support the notion that physical readiness and psychological readiness should be examined and treated as independent factors during ACLR rehabilitation among young athletes.
Effect of Age
Age has been identified as a significant factor in successful RTS after ACLR, with younger athletes more likely to return to their preinjury sport. 3 In this study, every 1 year increase in age was associated with an estimated mean decrease in ACL-RSI scores by approximately 1 to 3 points, indicating worse scores among older participants. These findings are supported by previous work from Webster et al, 30 which found younger age to have a positive effect on psychological readiness. In addition, McPherson et al 22 reported that a smaller change in psychological readiness across the timecourse of rehabilitation led to an increased risk of a second ACL injury among young athletes. Collectively, these findings emphasize the importance of monitoring psychological readiness throughout rehabilitation, particularly among young athletes.
Of note, a significant difference in age was found between the SPORT EXP-YES and SPORT EXP-NO groups. While exposure to preinjury level of sport was associated with higher ACL-RSI scores, the SPORT EXP-YES group also consisted of younger athletes. It is possible that participants of a younger age may have more opportunity to participate in preinjury level of sport by time of RTS clearance.
Effect of Sex
Differences in ACL injury incidence and RTS rates are prevalent between sexes, with female athletes often demonstrating worse outcomes.7,23,25,30 The results from this study show that young males demonstrate mean ACL-RSI scores (overall score and Emotions subscale) estimated to be approximately 12 to 16 points higher than that of young female athletes. Webster et al 30 also found that young female athletes report lower psychological readiness, while male sex was associated with higher psychological readiness at 12 months post-ACLR. Yet, contrary to these findings, Kuenze et al 18 found no difference between the sexes and their respective ACL-RSI scores. Methodological differences may contribute to these conflicting findings. Kuenze et al 18 administered the ACL-RSI questionnaire at an average of 7 months after ACLR, while the sex-based differences in ACL-RSI scores were found among athletes who completed the ACL-RSI at a later time point, including those in the current study.18,30 These findings may indicate that the final phase of rehabilitation before RTS is a critical time for adolescent female athletes, warranting further investigation.
Limitations
There are significant limitations to consider for this study. Interactions between independent variables were not considered due to sample size. As a result, these findings may not accurately represent true relationships between strength, sport exposure, sex, and age. Sport exposure data were collected from a self-reported survey and did not assess intensity, type, or exact amount of time the athlete participated in their respective sport. Second, our population is limited to adolescents aged 15 to 25 years, which is not reflective of the general population who may undergo ACLR. In addition, the ACL-RSI has been identified as a valid and reliable measure of psychological readiness in adults. 29 Due to the relatively high ACL-RSI scores of this cohort, future assessment of the validity of the ACL-RSI in an adolescent population is warranted. Furthermore, the majority of our cohort was female. This is reflective of the young adolecent population undergoing ACLR, as there is evidence that female adolecents are at a higher risk of ACL injury than their male counterparts. 7 Last, this study was a cross-sectional view of outcomes among young athletes in the weeks after medical clearance to RTS. The findings from this approach provide important insight into the variables of strength, sport exposure, and psychological readiness, but do not infer directionality due to study design.
Conclusion
Exposure to preinjury level of sport participation in the weeks after medical clearance to RTS after ACLR was associated with higher psychological readiness among young athletes, while isometric quadriceps strength was not. Clinicians should be encouraged to evaluate and treat physical and psychological constructs separately.
Supplemental Material
Supplemental material, sj-docx-1-sph-10.1177_19417381231223522 for The Influence of Strength and Sport Exposure on Psychological Readiness After ACL Reconstruction by Griffin P. Zink, Christin M. Zwolski, Staci M. Thomas, Mark V. Paterno and Laura C. Schmitt in Sports Health
Footnotes
The following authors declared potential conflicts of interest: L.C.S. has received speaking payments from the ACL Research Retreat. S.M.T. has received consulting fees from Emory University Healthcare.
The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: 2019 AOSSM/Aircast RTS Research Award.
ORCID iDs: Christin M. Zwolski 
https://orcid.org/0000-0002-5924-6051
Staci M. Thomas
https://orcid.org/0000-0003-2215-7319
Mark V. Paterno
https://orcid.org/0000-0003-2997-5023
Laura C. Schmitt
https://orcid.org/0000-0003-3813-6395
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Supplementary Materials
Supplemental material, sj-docx-1-sph-10.1177_19417381231223522 for The Influence of Strength and Sport Exposure on Psychological Readiness After ACL Reconstruction by Griffin P. Zink, Christin M. Zwolski, Staci M. Thomas, Mark V. Paterno and Laura C. Schmitt in Sports Health