Sports Health: A Multidisciplinary Approach

Oral contraceptives (OCs) manipulate hormonal fluctuations of the menstrual cycle and affect physical performance. Most investigations on the effect of OCs on physical performance did not discriminate between different types of OCs. Thus, the effects of monophasic OCs (MOCs) - the most common type of OCs - on muscle strength and recovery from exercise are largely unknown.

To examine the effect of MOC use on muscle strength and markers of recovery after exercise-induced muscle damage (EIMD) in premenopausal women.

Electronic databases Embase, PubMed, SportDiscus, and Web of Science were searched for studies examining the effect of MOCs on acute muscle strength and recovery.

Keywords applied for the study selection were oral contraceptive* AND muscle strength or oral contraceptive* AND muscle damage.

Systematic review.

Lowest quality assessed for an included study in this review was serious risk of bias using ROBINS-I tool made from Cochrane for nonrandomized studies.

A total of 104 studies on muscle strength were identified, of which 11 met the inclusion criteria. Concerning recovery, 51 studies were identified, of which 4 met the inclusion criteria.

Of the 11 studies included, 10 showed no effect of MOCs on acute muscle strength. Of the 4 studies on recovery, 2 found a greater decrease in muscle strength, and 3 found higher creatine kinase (CK) levels after EIMD in MOC users than in nonusers. The included studies were all rated with moderate-to-serious risk of bias.

These findings suggest that MOCs may impair recovery from EIMD as indicated by lowered muscle strength and elevated CK levels. There is insufficient evidence to conclude whether MOCs acutely affect muscle strength. Moderate-to-serious risk of bias in studies makes interpretation challenging.

Despite increasing use of reference values in isokinetic measurements and increasing importance, there is no systematic review of the reference values for lower and upper limb isokinetic muscle strength.

A systematic review to analyze studies on the reference values and protocols for the measurement for upper and lower limb isokinetic muscle strength in an untrained and noninjured healthy population.

MEDLINE, Scopus, Scielo, and CINAHL (from the earliest date available to June 2020).

Studies that measured a set of reference values for isokinetic muscle strength.

Systematic review.

Level 3.

Two reviewers selected studies independently. Data related to participants characteristics, outcomes of interest, isokinetic parameters, reference values for isokinetic muscle strength, and quality of evidence assessment were systematically reviewed independently by 2 authors.

A total of 31 studies met the study criteria. The included studies were used to synthesize the isokinetic muscle strength data according to age-group and sex. We extracted 1845 normative data related to isokinetic strength. Of these, 1181 items referred to lower limbs and 664 items to upper limbs.

In general, agonist muscle groups are stronger than antagonist muscles, and the men tend to obtain higher strength values than women. The angular velocity varied from 10 to 300 deg/s. The reference values identified can be useful for professionals to obtain during the isokinetic evaluation of the diagnostic parameters of muscle deficiency.

Using lifting straps during pulling exercises (such as deadlift) may increase absolute velocity performance. However, it remains unclear whether lifting straps could also reduce the degree of relative fatigue measured by velocity decline and maintenance in a training set.

There will be less mean velocity decline (MVD) and greater mean velocity maintenance (MVM) for deadlifts performed with (DLw) compared with without (DLn) lifting straps, and an underestimation of MVD and MVM when using the first compared with the fastest repetition as a reference repetition.

Randomized cross over design.

Level 3.

A total of 16 resistance-trained men performed a familiarization session, 2 1-repetition maximum [1RM] sessions (1 with and 1 without lifting straps), and 3 randomly applied experimental sessions consisting of 4 sets of 4 repetitions: (1) DLw against the 80% of DLn 1RM (DLwn), (2) DLn against the 80% of the DLn 1RM (DLnn), and (3) DLw against the 80% of the DLw 1RM (DLww). MVD and MVM were calculated using the first and the fastest repetition as the reference repetition.

MVD was significantly lower during DLwn and DLnn compared with DLww (P < 0.01), whereas MVM was greater during DLwn and DLnn compared with DLwn (P < 0.01) with no differences between DLwn and DLnn for both MVD and MVM (P > 0.05). The second repetition of the set was generally the fastest (54.1%) and lower MVD and higher MVM were observed when the first repetition was used as the reference repetition (P < 0.05).

Lifting straps were not effective at reducing MVD and increasing MVM when the same absolute loads were lifted. Furthermore, using the first repetition as the reference repetition underestimated MVD, and overestimated MVM.

The fastest repetition should be used as the reference repetition to avoid inducing excessive fatigue when the first repetition is not the fastest.

The posterior scapular muscles eccentrically contract to disperse the high forces observed in the deceleration phase of pitching. Muscular adaptations often occur following chronic eccentric loading, however, no study has evaluated the adaptations of the posterior scapular muscles with regard to throwing and their relationship with humeral retroversion (HR) in professional pitchers.

Significant chronic adaptations in muscle thickness (MT) and strength of the trapezius and rhomboids would be observed in healthy professional baseball pitchers, and there would be a significant relationship between humeral adaptations (ie, HR) and posterior scapular muscle adaptations (ie, strength and MT).

Cross-sectional; Level 3.

A total of 28 healthy male professional baseball pitchers (age, 22 ± 2 years; mass, 95 ± 17 kg; height, 190 ± 7 cm) were included in the study. Bilateral isometric muscle strength of the upper trapezius (UT), middle trapezius, lower trapezius (LT), and rhomboids was measured during a maximum voluntary isometric contraction. Diagnostic ultrasound images of the UT, middle trapezius, LT, rhomboid major, and rhomboid minor muscles were collected bilaterally to measure MT. HR was also quantified bilaterally with ultrasound. Paired sample t tests were used to compare dominant and nondominant strength and MT. Pearson correlation coefficients were used to assess the relationship between HR, isometric strength, and MT.

A significantly increased MT of the LT was found on the dominant arm compared with the nondominant arm (5.4 ± 1.1 mm vs 4.4 ± 1.5 mm; P = 0.00). The Pearson correlation coefficient demonstrated a significant weak negative relationship between HR and rhomboid major MT (P = 0.03; R = −0.36), and a significant weak negative correlation between HR and middle trapezius isometric strength (P = 0.03; R = −0.37).

LT thickness was greater in the throwing arm compared with the nonthrowing arm of pitchers, suggesting a positive adaptation of the LT. Interestingly, there was a weak negative relationship between HR and both rhomboid major MT and middle trapezius isometric strength. This negative relationship suggests that since increased HR leads to decreased internal rotation range of motion during deceleration, the scapula may be forced into anterior tilt and protraction, which can place excessive eccentric load on the rhomboid major and middle trapezius.

Maintaining scapular mechanics is important for upper extremity functionality and posture. Determining the extent to which the scapular stabilizer muscles affect the scapular position may guide the creation of an exercise program for people with scapular dyskinesis.

The serratus anterior (SA), upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) muscles play different roles on scapular position when humeral elevation increase.

Cross-sectional study.

Level 4.

A total of 70 women aged 40 to 65 years (mean age, 49 ± 7 years) who met the inclusion criteria were included in the study. Isometric muscle strength of the SA, UT, MT, and LT was evaluated with a handheld dynamometer. For assessment of scapular position, the lateral scapular slide test (LSST) was used. Multiple stepwise regression analysis was used to evaluate scapular parameters.

There were positive and statistically significant correlations between the isometric muscle strength of the SA, UT, MT, and LT muscles and the values at different humerus positions in the LSST (P < 0.05). The UT and SA muscles greatly affected the changes in the position of the inferior region of the scapula (R² > 24.5%). The LT (11.3%) in neutral position, MT (25.4%) with arm abducted at 45°, and SA (34.5%) with arm abducted 90° had a major effect on the changes in the mediolateral position of the scapula.

While the LT muscle affects the mediolateral position of the scapula to a large extent, the strength of the MT and SA muscles becomes effective as the shoulder elevation increases. SA and UT muscle strength have a greater effect on the position of the inferior region of the scapula.

Dyskinesis can be observed at different levels of the scapula; therefore, it is important to determine at which level the dyskinesis is more prominent for each individual and consequently to form a personalized exercise program to increase function and control dyskinesis.

Muscle atrophy is common after an injury to the knee and anterior cruciate ligament reconstruction (ACLR). Blood flow restriction therapy (BFR) combined with low-load resistance exercise may help mitigate muscle loss and improve the overall condition of the lower extremity (LE).

To determine whether BFR decreases the loss of LE lean mass (LM), bone mass, and bone mineral density (BMD) while improving function compared with standard rehabilitation after ACLR.

Randomized controlled clinical trial

A total of 32 patients undergoing ACLR with bone-patellar tendon-bone autograft were randomized into 2 groups (CONTROL: N = 15 [male = 7, female = 8; age = 24.1 ± 7.2 years; body mass index [BMI] = 26.9 ± 5.3 kg/m2] and BFR: N = 17 [male = 12, female = 5; age = 28.1 ± 7.4 years; BMI = 25.2 ± 2.8 kg/m2]) and performed 12 weeks of postsurgery rehabilitation with an average follow-up of 2.3 ± 1.0 years. Both groups performed the same rehabilitation protocol. During select exercises, the BFR group exercised under 80% arterial occlusion of the postoperative limb (Delfi tourniquet system). BMD, bone mass, and LM were measured using DEXA (iDXA, GE) at presurgery, week 6, and week 12 of rehabilitation. Functional measures were recorded at week 8 and week 12. Return to sport (RTS) was defined as the timepoint at which ACLR-specific objective functional testing was passed at physical therapy. A group-by-time analysis of covariance followed by a Tukey’s post hoc test were used to detect within- and between-group changes. Type I error; α = 0.05.

Compared with presurgery, only the CONTROL group experienced decreases in LE-LM at week 6 (−0.61 ± 0.19 kg, −6.64 ± 1.86%; P < 0.01) and week 12 (−0.39 ± 0.15 kg, −4.67 ± 1.58%; P = 0.01) of rehabilitation. LE bone mass was decreased only in the CONTROL group at week 6 (−12.87 ± 3.02 g, −2.11 ± 0.47%; P < 0.01) and week 12 (−16.95 ± 4.32 g,−2.58 ± 0.64%; P < 0.01). Overall, loss of site-specific BMD was greater in the CONTROL group (P < 0.05). Only the CONTROL group experienced reductions in proximal tibia (−8.00 ± 1.10%; P < 0.01) and proximal fibula (−15.0±2.50%,P < 0.01) at week 12 compared with presurgery measures. There were no complications. Functional measures were similar between groups. RTS time was reduced in the BFR group (6.4 ± 0.3 months) compared with the CONTROL group (8.3 ± 0.5 months; P = 0.01).

After ACLR, BFR may decrease muscle and bone loss for up to 12 weeks postoperatively and may improve time to RTS with functional outcomes comparable with those of standard rehabilitation.

Quadriceps weakness is common after anterior cruciate ligament (ACL) reconstruction and can alter gait mechanics. Functional resistance training (FRT) is a novel approach to retraining strength after injury, but it is unclear how it alters gait mechanics. Therefore, we tested how 3 different types of FRT devices: a knee brace resisting extension (unidirectional brace), a knee brace resisting extension and flexion (bidirectional brace), and an elastic band pulling backwards on the ankle (elastic band)–acutely alter gait kinetics in this population.

The type of FRT device will affect ground-reaction forces (GRFs) during and after the training. Specifically, the uni- and bidirectional braces will increase GRFs when compared with the elastic band.

Crossover study.

Level 2.

A total of 15 individuals with ACL reconstruction received FRT with each device over 3 separate randomized sessions. During training, participants walked on a treadmill while performing a tracking task with visual feedback. Sessions contained 5 training trials (180 seconds each) with rest between. Vertical and anterior-posterior GRFs were assessed on the ACL-reconstructed leg before, during, and after training. Changes in GRFs were compared across devices using 1-dimensional statistical parametric mapping.

Resistance applied via bidirectional brace acutely increased gait kinetics during terminal stance/pre-swing (ie, push-off), while resistance applied via elastic band acutely increased gait kinetics during initial contact/loading (ie, braking). Both braces behaved similarly, but the unidirectional brace was less effective for increasing push-off GRFs.

FRT after ACL reconstruction can acutely alter gait kinetics during training. Devices can be applied to selectively alter gait kinetics. However, the long-term effects of FRT after ACL reconstruction with these devices are still unknown.

FRT may be applied to alter gait kinetics of the involved limb after ACL reconstruction, depending on the device used.

Patellar tendinopathy (PT), or jumper’s knee, is a chronic painful overuse patellar tendon injury. For PT, prevention is more important than treatment. However, there is still a lack of strong evidence to confirm the effectiveness of prevention.

This study will analyze by meta-analysis the effect of a prophylactic program on high PT risk people (but without PT) in reducing PT occurrence.

PubMed, Embase, the Cochrane Library, Scopus, and Ebscohost, from inception to January 11, 2022.

A study comparing the effects of prophylactic programs and controls on the risk of PT was included in the analysis. After a database search with search terms ((patellar tendinopathy) OR (jumper’s knee) OR (patellar tendinitis) OR (patellar tendinosis) OR (patellar tendonitis)) AND ((Prevent*) OR (prophyla*)), a total of 1444 items were obtained. Of these, 11 studies with 6091 participants were eligible for inclusion in this meta-analysis.

Systematic review and meta-analysis.

Level 2.

The first author’s name, publication year, study design, country, population, mean age, sex, prophylactic program, control, study duration, and the frequency or incidence of PT in each group were extracted.

A total of 11 articles were included in the analysis. Overall, no significant difference was considered in the risk of PT between the prophylactic program and control groups based on the random-effect model (odds ratio [OR], 0.85; 95% CI, 0.67, 1.08; P = 0.18). In the recruit subgroup, there was even a tendency to elevate the risk of PT occurrence after prophylaxis was executed (OR, 1.89; 95% CI, 0.68, 5.28; P = 0.22). In athletes, the prophylactic program tended to decrease the risk of PT compared with the control (OR, 0.81; 95% CI, 0.63, 1.04; P = 0.10); however, the difference was not statistically significant. Trial sequential analysis results suggested that prophylaxis may still be effective for athletes, but this needs to be confirmed with a larger sample size.

The risk of PT cannot be reduced with the current prophylactic program. However, for athletes, the negative results may be due to insufficient sample size.

Neuromuscular training (NMT) has demonstrated efficacy as an intervention to decrease the risk of anterior cruciate ligament injuries and improve sports performance. The effect of this training on the mechanisms that contribute to improved physical performance has not been well defined.

Athletes in the NMT group will have better mechanisms of fundamental movements and agility tests that may contribute to improved sports performance.

Prospective cohort study

Level 2

Eight high school teams (111 athletes, 53% male, mean age 16 years) participated, with half performing NMT. Physical performance was measured using the dorsaVi ViPerform system, a US Food and Drug Administration-cleared wireless sensor system. Agility was assessed using a timed 3-cone test. Independent sample t tests were used to compare differences between the intervention and control groups.

Matched pre- and postseason data were collected from 74 athletes after excluding athletes with injury and those lost to follow-up. Significant improvements were observed in the NMT group for loading/landing speed ratios during a single-leg hop test (right lower extremity = −0.19 [–0.37, 0.03], P = 0.03 and left lower extremity = −0.27 [–0.50, −0.03], P = 0.03). The control group had lower ground reaction forces compared with the NMT group (P < 0.02), while significant improvements were found in the NMT group for initial peak acceleration (P < 0.02) and cadence (P = 0.01) during a straight-line acceleration/deceleration test. For the 3-cone agility test, the postseason time decreased compared with preseason in the NMT group, whereas the time for the control group increased (–0.37 s vs 0.14 s, P < 0.00).

The results demonstrate that NMT administered by sports medicine clinicians can significantly improve some physical performance of fundamental movements in high school athletes.

Coaches should be trained to effectively deliver NMT in order to improve sports performance.

The Fédération Internationale de Football Association (FIFA) 11+ Kids is an exercise-based injury prevention program developed by an international group of experts to prevent injuries among child soccer players.

It was hypothesized that the FIFA 11+ Kids program would be more effective than performing a typical warm-up regimen in reducing overall injuries among soccer players aged 7 to 13 years.

A clustered randomized controlled trial.

Level 1.

A total of 94 boys’ soccer teams, including 780 players, were randomly allocated into an experimental or control group. Complete datasets were collected from 45 teams (377 players) and 43 teams (363 players) in the experimental and control groups, respectively. The experimental group underwent the FIFA 11+ Kids program as a warm-up during training sessions and matches at least twice a week, and the control group continued performing their usual warm-ups. Participants were prospectively followed during 1 season (6 months). The primary outcomes included the incidence of overall and recurrent injuries and their mechanism and severity. The secondary outcome was the rate of compliance with the intervention program.

A total of 43 injuries were reported in the experimental group in 50,120 hours of exposure (0.85 injuries/1000 exposure hours). A total of 86 injuries were reported in the control group in 42,616 hours of exposure (2.01 injuries/1000 exposure hours). The injury risk ratio was 0.43 (0.29-0.61), suggesting that the experimental group experienced 57% fewer injuries than those in the control group.

The FIFA 11+ Kids program reduced overall injury rates in children playing soccer more than the usual warm-ups.

The results of this study provide evidence for children’s coaches to consider including the FIFA 11+ Kids program in their warm-up regimen. Such a program may prevent injury risk and decrease absenteeism and injury-related financial burdens.

The Dynamic Exertion Test (EXiT) was developed to inform return-to-play (RTP) decision-making following clinical recovery from sport-related concussion (SRC). The purpose of the current study was to document intrarater and test-retest reliability and minimal detectable change (MDC) scores for physiological [heart rate (HR) and blood pressure], performance (change-of-direction task completion time and errors), and clinical outcomes (endorsed symptoms, perceived exertion) of EXiT, and interrater reliability of performance outcomes.

Healthy athletes would exhibit stable physiological responses to the EXiT across visits, demonstrate consistent change-of-direction task completion time between consecutive trials at each visit, and the fastest time (of 2 trials) across visits, and endorse equivocal symptoms and effort across visits.

Cross-sectional, test-retest.

Level 3.

Seventy-nine (female: 34 [43%], 19.6 ± 5.0 years) athletes completed the EXiT at 2 study visits (8.7 ± 4.7 days between visits). Two-way, mixed, intraclass correlation coefficients (ICCs) were used to evaluate intrarater and test-retest reliability. Cronbach’s alpha was used to document the internal consistency of symptoms at each visit, and MDC scores were calculated on the physiological, performance, and clinical outcomes.

Measured and percentage of age-estimated maximum HR were reliable following EXiT (ICC = 0.579-0.618). Change-of-direction task completion time (MDC range = 0.75-8.70 s) had good-to-excellent test-retest (ICC = 0.703-0.948) and interrater (ICC = 0.932-0.965) reliability. Symptoms had a high internal consistency at visits 1 (α = 0.894) and 2 (α = 0.805) and were reliable across visits (ICC = 0.588).

The current investigation established test-retest reliability in addition to MDC scores of an objective dynamic exercise assessment among healthy adolescent and adult athletes. The EXiT may be an objective approach to inform RTP decision-making following SRC recovery.

The EXiT is a clinically feasible exertion-based assessment that can be readily administered in a variety of outpatient clinical settings.

Little data exist regarding the association of slipped capital femoral epiphysis (SCFE) and sporting activities.

There is no association between SCFE and sporting activities.

Retrospective review of all SCFE cases at our institution from 2010 through March 2021.

Level 3.

All patients with idiopathic SCFE were reviewed looking for the presence/absence of sporting activities and symptom onset. Also collected were the age, symptom duration, and weight/height of the patient, sex, race, and stable/unstable nature of the SCFE. The severity of the SCFE was measured using the lateral epiphyseal-shaft angle.

There were 193 children (110 boys, 83 girls) with idiopathic SCFEs. The SCFE was stable in 147, unstable in 45, and unknown in 1. The average age was 12.1 ± 1.8 years, average SCFE angle 38° ± 20° and symptom duration 4.0 ± 5.1 months. An association with a sporting activity was present in 64 (33%). The sporting activity was basketball (18), football (11), baseball/softball (10), and others (23). Football, basketball, and soccer predominated in boys, baseball and running sports were equal between boys and girls, and cheerleading/gymnastics/dancing predominated in girls. Differences showed that those involved in sports had a slightly lower body mass index (BMI) (88th percentile vs 95th percentile, P = 0.00). There were no differences between those involved and those not those involved in sporting activities for symptom duration, SCFE severity, sex, race, or stable/unstable SCFE type.

Sporting activities are associated with the onset of symptoms in 1 of 3 of patients with SCFE, refuting the null hypothesis.

A high level of suspicion for SCFE should be given when any peripubertal athlete presents with hip or knee pain regardless of BMI/obesity status, and appropriate imaging performed.

The Balance Error Scoring System (BESS) is commonly accepted as a valid measure of postural stability. However, reliability values have varied, and subtle changes undetectable with the human eye may exist postinjury. The inertial measurement unit in commercially available tablets has been used to quantify postural sway (instrumented Balance Error Scoring System [iBESS] volume). However, iBESS has not been validated in a military population, and the stability of the tests beyond 1 week is unknown.

iBESS volume is capable of objectively measuring postural sway during the traditional BESS.

Prospective repeated-measures study.

Level 3.

Eighty-three cadets (40.96% women; age 20.0 ± 1.44 years; height 68.7 ± 4.1 inches; weight 166.7 ± 30.2 lb) with no history of concussion or lower extremity injury agreed to participate. All participants completed the BESS at baseline and 6 months post baseline. During testing, a tablet equipped with an inertial measurement unit was positioned on the participant’s sacrum to capture postural sway.

Moderate to strong correlations were exhibited between baseline measurements for single-limb (SL)-firm (r = 0.84; P < 0.01), tandem (TAN)-firm (r = 0.85; P < 0.01), double-limb (DL)-foam (r = 0.50; P < 0.01), SL-foam (r = 0.59; P < 0.01), and TAN-foam (r = 0.79; P < 0.01). Balance improved significantly at 6 months for SL-firm human-rated errors (Effect Size [ES] = 0.32) and for SL-firm (ES = 0.38), DL-foam (ES = 0.21), and SL-foam iBESS volume (ES = 0.35). Moderate to strong correlations were exhibited between human-rated and iBESS change scores for SL-firm (r = 0.71; P < 0.01), TAN-firm (r = 0.75; P < 0.01), and TAN-foam (r = 0.71; P < 0.01), and a weak correlation was exhibited for DL-foam (r = 0.29; P < 0.01) and SL-foam (r = 0.40; P < 0.01).

Moderate to strong correlations existed between human-rated BESS errors and iBESS volume at baseline and between change scores. In addition, iBESS volume may be more sensitive to balance changes than the human-rated BESS.

This evidence supports the use of iBESS volume as a valid measure of postural stability in military cadets. iBESS volume may provide clinicians with an objective and more sensitive measure of postural stability than the traditional human-rated BESS.

A comprehensive understanding of the intrinsic risk factors for anterior cruciate ligament (ACL) disruption is important for identifying individuals at increased risk for suffering this trauma and developing interventions to mitigate risk.

A variety of risk factors predispose athletes to first-time, noncontact ACL injury and some of these differ between male and female athletes.

Prospective cohort study with nested case-control sampling.

Level 2.

Sport teams at 28 high schools and 8 colleges were monitored prospectively over 4 years, and 109 of 130 athletes who suffered their first noncontact ACL injury participated in the study. At the time of injury, matched control subjects were randomly selected from among the case’s teammates and a total of 227 athletes participated. Demographic characteristics, joint laxity, lower extremity alignment, strength, and personality characteristics were measured. The association of each risk factor with injury risk was assessed by conditional logistic regression.

The risk factors that were associated with ACL injury in both male and female athletes included having a parent with prior ACL injury and increases of the following variables: body weight, anterior displacement of the tibia relative to the femur, genu recurvatum, and generalized joint laxity. Risk factors that are unique to female athletes included increased body mass index, increased trunk flexion strength, and prior non-ACL knee injury. The risk factors specific to male athletes were decreased standing quadriceps angle, decreased hip adduction strength, and chronic disease.

A diverse set of risk factors predispose both male and female athletes to ACL injury, whereas others appear to be sex-specific.

Different approaches for assessing risk and preventing ACL injury are needed for male and female athletes. In addition, personalized prevention strategies may be needed to target the specific characteristics that place an individual at increased risk of suffering this trauma.

Many studies have analyzed gymnastics-related injuries in collegiate and elite athletes, but there is minimal literature analyzing the epidemiological characteristics of injuries in the greater gymnastics community.

A higher incidence of injuries in younger gymnasts between the ages of 6 and 15 years compared with those 16 years and older and a difference in the distribution of injuries between male and female gymnasts.

Retrospective cross-sectional study.

Level 3.

The National Electronic Injury Surveillance System (NEISS) was queried for all gymnastics-related musculoskeletal injuries presenting to the emergency department (ED) between 2013 and 2020. Incidence was calculated as per 100,000 person-years using the weighted estimates provided by NEISS and national participation data. Chi-square and column proportion z-testing was used to analyze where appropriate.

The incidence of gymnastics-related musculoskeletal injuries was 480.7 per 100,000 person-years. Most ED visits were children between the ages of 6 and 15 years (84.0%). Younger gymnasts (ages 6 to 10) were most likely to experience a lower arm fracture, while those over the age of 10 years were most likely to experience an ankle sprain (P < 0.01). Men and boys presented with a much greater proportion of shoulder injuries (8.0% vs 3.9%), while women and girls presented with a greater proportion of elbow injuries (9.9 % vs 5.9%) and wrist (10.5% vs 8.3%) injuries (P < 0.01).

As hypothesized, most gymnastics-related injuries between 2013 and 2020 were athletes between 6 and 15 years old. Many of these athletes are attempting new, more difficult, skills and are at increased risk of more acute injury when attempting skills they may be unfamiliar with.

With increased pressure to specialize at an early age to maintain competitiveness and learn new, higher-level skills compared with their peers, younger athletes are most susceptible to acute injury. New injury prevention strategies could be implemented to help this high-risk population compete and train safely.

The countermovement jump (CMJ) is a valid and reliable test of lower extremity (LE) muscle power. However, the CMJ may not be appropriate during early-stage rehabilitation of injuries. Functional muscle strength tests (FMSTs) could evaluate LE muscle power with lower joint reaction forces.

The lateral step-up test (LSUT), 5 times sit to stand (5×STS), and 30-s chair stand test (30CST) could predict CMJ jump height (JHt) and jump peak power (JPow).

Cross-sectional study.

Level 2.

Eighty-one young adults performed 3 CMJs to measure JHt and JPow using an electronic jump mat and speed analyzer. Participants also performed three FMSTs: 1 trial of the LSUT and a modified trial of LSUT touching the ground with the heel only (MLSUT); 2 trials of the 5×STS; and 2 trials of the 30CST, in a randomized order. Spearman rho correlations and hierarchal multiple linear regressions were used to determine whether FMST performances predicted JHt and JPow, after controlling for sex, body height, and body mass.

30CST, LSUT, MLSUT, sex, body mass, and body height were significantly associated with JHt (P < 0.05). LSUT, sex, body height, and body mass were significantly associated with JPow (P < 0.05). Hierarchical regression analyses showed that the 30CST significantly predicted JHt (P < 0.01) and JPow (P = 0.03), independent of sex, body height, and body mass.

30CST performance predicted JHt and JPow in young adults.

The 30CST is easy to perform, requires equipment found readily in clinics, and predicts LE muscle power. This test could be used to track progress during the early stages of LE injury rehabilitation.