Isometric Hamstring Strength Research Articles

Implementing the Copenhagen Adductor Exercise and Nordic Hamstring Exercise in West African Academy Soccer Players: An Intervention Study.

This study implemented the Copenhagen Adductor Exercise (CAE) and Nordic Hamstring Exercise (NHE) to examine 1) whether CAE and NHE interventions are associated with adductor and hamstring strength gains in youth African male soccer players and 2) whether strength changes after a rest period and secondary intervention. Pre-post intervention study. Forty-four African elite male academy players (age 14.7±1.5 [12-18] years) participated in twice weekly CAE and NHE interventions for 8- and 10-week periods separated by a 4-week rest. Long lever adductor squeeze strength and prone isometric hamstring strength were measured with mixed-effects linear regression models to observe strength changes over time. Ninety-six and 95% of CAE and NHE sessions were completed in each intervention, with no adverse events related to the execution of the exercises. Adductor squeeze strength increased during the first intervention (baseline 3.23 [2.99-3.47] N/kg, post-intervention 3.53 [3.30-3.76] N/kg, p=0.911) and was maintained following the rest period (3.52 [3.27-3.76] N/kg, p=0.999) and second intervention (3.60 [3.35-3.84] N/kg, p=0.002). Hamstring strength improved during the first intervention (baseline 4.95 [4.42-5.49] N/kg, post-intervention 5.48 [4.95-6.02] N/kg, p<0.001), decreased to baseline during the rest period (4.98 [4.44-5.53] N/kg, p=0.996), and did not improve during the second intervention (5.01 [4.46-5.55] N/kg, p=0.978). CAE and NHE interventions can be implemented at an elite African academy with high compliance. Adductor and hamstring strength improved in the first intervention, with no further improvements in the second intervention. Secondary interventions therefore should include higher exercise volume or load to improve longitudinal adductor and hamstring strength. Level III (Cohort Study).

Bridge-Enhanced Anterior Cruciate Ligament Restoration: 6-Year Results From the First-in-Human Cohort Study.

Bridge-enhanced anterior cruciate ligament restoration (BEAR) combines suture repair of the anterior cruciate ligament (ACL) with an extracellular matrix implant plus autologous blood to facilitate native ACL healing. The purpose of this study was to compare the 6-year follow-up outcomes of patients who underwent the BEAR procedure with those of a nonrandomized concurrent control group receiving autograft ACL reconstruction (ACLR) in the first-in-human safety study of the BEAR implant (BEAR I trial). Based on the 2-year results, it was hypothesized that isometric hamstring strength after the BEAR procedure would be greater than that after ACLR and that there would be no other differences in outcomes at 6 years. Cohort study, Level of evidence, 2. Ten patients underwent BEAR and 10 received ACLR with a 4-stranded hamstring autograft. Outcomes assessed included the record of subsequent surgeries, the International Knee Documentation Committee (IKDC) Subjective Knee Score, IKDC physical examination grade, the Knee injury and Osteoarthritis Outcome Score, instrumented knee laxity, functional outcomes (ie, muscle strength assessments and hop testing), and qualitative magnetic resonance imaging assessment. Comparisons between treatments were based on computations of the mean differences and the associated 95% CIs. One patient in the BEAR group and 3 patients in the ACLR group were lost to follow-up. In the period between 2 and 6 years, 1 patient in each group underwent revision surgery. There were no differences between groups at the 6-year follow-up in any of the outcome measures except for isometric hamstring strength, which was approximately equal to that of the contralateral knee in the BEAR group and <44% of that in the contralateral knee in the ACLR group (P < .01). This preliminary study suggests that the outcomes of BEAR and ACLR with a hamstring tendon graft may be similar at the 6-year follow-up and warrants investigation of the BEAR procedure in a larger cohort of patients.

Operative Repair of Hamstring Injuries From the Jackling Position in Rugby.

The jackling position within rugby has not been previously described as a mechanism for proximal hamstring injuries. Acute surgical repair of proximal hamstring avulsion injuries sustained from the jackling contact position enables a return to a previous level of sporting activity with low risk of recurrence. Case series; Level of evidence, 4. This study included 54 professional rugby players (mean age, 26 ± 4.8 years) who underwent acute primary surgical repair of complete, proximal hamstring avulsion injuries. The mean follow-up time was 17 months (range, 12-24 months). Mean isometric hamstring strength and function testing was performed at 3 months and 1 year after repair. Of the 54 players, 51 (94.4%) returned to their preinjury level of sporting activity. The mean time from surgical repair to full sporting activity was 7 months (range, 4-12 months). No patients had recurrence of the primary injury. At 1 year postoperatively, patients had significantly restored mean isometric hamstring muscle strength when compared with the uninjured leg at 0° (98.4% ± 2.8%), 15° (95.9% ± 2.9%), and 45° (92.9% ± 4.1%); improved Lower Extremity Functional Score (78.0 ± 2.0); and improved Marx activity rating score (14.3 ± 1.5) (P < .001 for all). Acute surgical repair of proximal hamstring avulsion injuries caused by the contact jackling position produced a high return to preinjury level of sporting activity, increased muscle strength, and improved functional outcome scores, with a low risk of recurrence at short-term follow-up.

A RANDOMIZED CONTROLLED TRIAL ASSESSING A BRACE-FREE AND ACCELERATED WEIGHT-BEARING PROTOCOL AFTER SURGICAL REPAIR OF ACUTE PROXIMAL HAMSTRING TENDON AVULSIONS

INTRODUCTION &amp; AIMS Proximal hamstring tendon avulsion from the ischial tuberosity is a significant injury, with surgical repair advocated. After surgery, limited data exists regarding the optimal rehabilitation regime with extensive variation in published protocols. This study investigated patient outcomes following a traditionally conservative (CR) versus accelerated (AR) rehabilitation regimen after proximal hamstring tendon repair. METHODS This prospective randomized controlled trial (RCT) allocated 50 patients undergoing proximal hamstring tendon repair to either a braced, partial weight-bearing rehabilitation regime (CR=25) or an accelerated, unbraced regime, that permitted full weight-bearing as tolerated (AR=25). Patients were evaluated pre-operatively and at 3, 6 and 12 months post-surgery, via patient-reported outcome measures (PROMs) including the Lower Extremity Functional Scale (LEFS), Perth Hamstring Assessment Tool (PHAT) and 12-item Short Form Health Survey (SF-12). The single (SHD), triple (THD) and triple crossover (TCHD) hop tests were assessed at 6 and 12 months, as was peak isometric hamstring strength and peak isokinetic knee extensor and flexor torque. RESULTS All PROMs improved (p&amp;gt;0.05) and, while the AR group reported a significantly better Physical Component Score for the SF-12 at 3 months (p=0.022), as well as a lower severity of hamstring pain at 12 months (p=0.032), there were no other group differences. Peak isometric hamstrings strength and peak isokinetic quadriceps and hamstrings torque symmetry were all comparable between groups (p&amp;gt;0.05). While the AR group demonstrated significantly better (p=0.009) limb symmetry for the THD at 6 months, no other hop test differences were seen between groups. Three re-injuries have been observed (CR=2, AR=1). CONCLUSION After proximal hamstring repair surgery, post-operative outcomes following an accelerated rehabilitation regimen were largely comparable to a traditionally conservative

Effect of Sampling Frequency on a Unilateral Isometric Hamstring Strength Assessment Using Force Plates

AbstractThe purpose of this study was to determine the effect of sampling frequency on the 90–90° (90-degrees hip and knee flexion) isometric hamstring assessment. Thirty-three elite female soccer players (age: 18.7 ± 3.7 years; height: 158.3 ± 5.9 cm; body mass: 62.8 ± 5.5 kg) performed three unilateral trials on a single occasion of the 90–90° isometric hamstring assessment. Force-time data were collected using force plates at 1000 Hz and down sampled to 500-, 250-, and 100 Hz. Peak force (N), force (N) at 100- and 200 ms and average rate of force development (aRFD) (N/s) over a 100- and 200 ms epoch were calculated. A repeated measures of analysis of variance and effect size was used to compare means. Excellent absolute and good relative reliability was observed for peak force across all sampling frequencies. Force at 100- and 200 ms and aRFD over 100 ms and 200 ms resulted poor-moderate relative reliability and poor-excellent absolute reliability. No significant trivial differences were observed for peak force between sampling frequencies (P &gt; 0.05, Cohen’s d = 0.02–0.12). A significant difference (P &lt; 0.001) was identified in 500, 250 and 100 Hz, with small-moderate and small-large increases in force at set time points and aRFD, respectively, in comparison to 1000 Hz (d = 0.21–2.00). Higher sampling frequencies (&gt; 500 Hz) reduces the reliability of time dependent force characteristics, with minimal effect on peak force. Regular monitoring of peak force can be performed with higher sampling frequencies, but lower sampling frequencies would be beneficial to collect reliable rapid-force generating measures.

Isokinetic profiles of hamstring and quadriceps muscles in the police special force operators

Knee injuries are of concern to police. The aims of this study were to determine initial reference values for isokinetic knee extension and flexion in police special force operators to explore the conventional hamstring contraction (Hcon) quadriceps contraction (Qcon) ratio, and to determine the limb symmetry index of the quadriceps and hamstring muscles. Absolute and relative isokinetic torque of quadriceps and hamstrings were assessed in 10 police special force operators using an isokinetic dynamometer Con-Trex. Subjects performed maximal knee extension and flexion at a contraction velocity of 60°/s at 90° of knee flexion. Means, standard deviations, 95% confidence interval values, and effect sizes were calculated. A paired samples t-test was used to test the between-leg differences in absolute and relative torques of quadriceps and hamstring muscles and to test the between-leg difference in Hcon/Qcon ratios as well as strength asymmetries of quadriceps and hamstrings. Descriptive statistics revealed torque values similar to athletes, and paired sample t-tests showed no significant between-leg differences in torque values at a group level. Small effect sizes were observed between legs in both the absolute and relative peak torque of the hamstring muscles. While, on a group level, no Hcon/Qcon ratio disparity between legs or asymmetries were observed, individual results indicated a trend towards greater dispersion for the dominant leg and some individual results indicated an increased asymmetry in isometric strength of hamstrings. The study provides normative data for this unique police population and highlights the need for relative strength work in this population.

Acute effect of different doses of caffeinated chewing gum on exercise performance in caffeine-habituated male soccer players.

The ergogenic benefits of caffeine have been well established, but there is scarce research on its chewing gum form. The present research aimed to examine the effects of different doses (100 and 200 mg) of caffeinated chewing gum on muscle strength, vertical jump performance, and ball-kicking speed in trained male soccer players. In a double-blind, randomized counterbalanced, and crossover research design, 14 male soccer players (age = 22 ± 2 y; body mass = 74.2 ± 7.1 kg; height = 180.0 ± 6.8 cm; habitual caffeine intake = 358.9 ± 292.4 mg/day) participated in three experimental trials. In each trial, participants performed isometric handgrip strength, quadriceps and hamstring strength, ball-kicking speed, and 15 s countermovement jump test 10 min after chewing 100 mg (LCAF) or 200 mg (MCAF) of caffeinated gum or placebo (PLA). MCAF improved quadriceps strength (53.77 ± 5.77 kg) compared to LCAF (49.62 ± 8.81 kg, p = 0.048) and PLA (49.20 ± 7.20 kg, p = 0.032). However, neither LCAF nor MCAF had a significant effect on the isometric handgrip and hamstring strength, ball-kicking speed, and 15 s countermovement jump test (all p > 0.05). These findings support chewing gum as an alternative mode of caffeine administration which can be used as a nutritional ergogenic aid for trained soccer players, at least for quadriceps strength.

Strength symmetry after autograft anterior cruciate ligament reconstruction

ObjectiveTo compare postoperative isometric quadriceps strength indices (QI%) and hamstring strength limb symmetry indices (HI%) between partial thickness quadriceps tendon (pQT), full thickness quadriceps tendon (fQT), and bone-patellar-tendon bone (BPTB) autograft anterior cruciate ligament reconstruction (ACLR). MethodsPatients with primary ACLR with pQT, fQT, or BPTB autograft with the documentation of quantitative postoperative strength assessments between 2016 and 2021 were included. Isometric Biodex data, including QI% and HI% (calculated as the percentage of involved to uninvolved limb strength) were collected between 5 and 8 months and between 9 and 15 months postoperatively. ResultsIn total, 124 and 51 patients had 5–8- and 9–15-month follow-up strength data, respectively. No significant difference was detected between groups for sex. However, patients undergoing fQT were found to be older than those undergoing BPTB (24.6±7 vs 20.2±5; ​p = 0.01). There were no significant differences in the number of concomitant meniscus repairs between the groups (pQT vs. fQT vs. BPTB). No significant differences were detected in median (min–max) QI% between pQT, fQT, and BPTB 5–8 months [87 ​% (44%–130 ​%), 84 ​% (44%–110 ​%), 82 ​% (37%–110 ​%) or 9–15 months [89 ​% (50%–110 ​%), 89 ​% (67%–110 ​%), and 90 ​% (74%–140 ​%)] postoperatively. Similarly, no differences were detected in median HI% between the groups 5–8 months or 9–15 months postoperatively. ConclusionThe study was unable to detect differences in the recovery of quadriceps strength between patients undergoing ACLR with pQT, fQT, and BPTB autografts at 5–8 months and 9–15-months postoperatively. Level of evidenceIII.

Reliability of a Field-Based Test for Hamstrings and Quadriceps Strength Assessment in Football Players

Background: Field-based tests using portable devices are extremely helpful to assist physicians and coaches in the assessment of athletes’ muscle strength and for injury risk screening. The aim of this study was to investigate the reliability of a field-based test to assess unilateral hamstring and quadriceps isometric muscle strength in a nearly extended position (30° knee flexion) in football players. Methods: Nineteen male football players completed the field-based test on two separate occasions, one week apart, to produce a test–retest design. To complete the test, participants performed maximal isometric efforts on a custom-built bench with 30° of knee flexion and 90° of hip flexion while the force applied was measured with a portable load cell at 80 Hz. On each occasion, participants performed two 2 s maximal isometric repetitions intending to flex and extend the knee to assess hamstring and quadriceps strength, respectively. In each repetition, the force developed during the maximum voluntary isometric contraction (MVIC) and rate of force development (RFD) metrics for hamstring (H) and quadriceps (Q) were collected, and the H:Q ratio was calculated afterwards. Results: MVIC showed the highest reliability for the measurement of both hamstring and quadriceps strength (ICC &gt; 0.80, [95% CI: 0.55, 0.96]; CV &lt; 14%, [95% CI: 6.6, 20]) and for H:Q (ICC &gt; 0.75, [95% CI: 0.48, 0.95]; CV &lt; 15%, [95% CI: 8.9, 22.4]). RFD0–150 and RFD0–250 yielded moderate reliability values for hamstring strength (ICC = 0.78–0.86, [95% CI: 0.52, 0.94]; CV = 20–27%, [95% CI: 15, 39.7]). RFD0–50 presented the largest variability (ICC &lt; 0.80, [95% CI: 0.62, 0.95]; CV &gt; 25%, [95% CI: 19.2, 45.3]). Conclusions: The field-based test presented here provided reliable results for the measurement of maximal isometric hamstring and quadriceps strength and for the calculation of the H:Q ratio. However, the measurement of RFD with this test is less reliable. This test allows reliable field-based assessments of hamstring and quadriceps maximal isometric strength which can be helpful to identify muscle strength deficits and imbalances during injury prevention and management processes in football players.

Post-game recovery of isometric hamstring strength in a high-risk hamstring strain injury group throughout an Australian Football League season

ABSTRACT This study sought to investigate post-game hamstring strength recovery of 26 Australian Football League (AFL) players with a previous hamstring strain injury (HSI) across an AFL season. Maximal unilateral isometric knee flexion strength was assessed using an externally fixed dynamometer, and inter-session reliability was measured during the pre-season period. Linear mixed effects models investigated the influence of numerous variables on post-game hamstring strength decrement (relative change between initial weekly test and individual baseline) and individual within-week strength change following gameplay. The test demonstrated good inter-tester reliability (ICC = 0.81–0.88; CV = 6.73–7.33), and an acceptable level of error (MAE = 5.77–7.14%). Player as a random effect strongly influenced post-game strength decrement and within-week strength change (marginal R2 = 0.185–0.407; conditional R2 = 0.455–0.654). Within-week hamstring strength change was strongly determined by post-game strength decrement alone (estimate = 0.51, 95% CI = -0.66- -0.36 ; η2 = 0.32; P=<0.001) and in interaction with number of days post-game (estimate = 0.43, 95% CI = 0.20–0.66; η2 = 0.096; P=<0.001). This study shows the importance of early individual assessment of post-game hamstring strength in players with prior hamstring injury and could be valuable to inform post-game hamstring recovery in future applications.

Explosive hamstrings strength asymmetry persists despite maximal hamstring strength recovery following anterior cruciate ligament reconstruction using hamstring tendon autografts

PurposeTo investigate the differences in maximal (isometric and concentric peak torque) and explosive (rate of torque development (RTD)) hamstring and quadriceps strength symmetry between males and females during early- and late-phase rehabilitation after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts and to determine the interaction of time and sex on maximal and explosive strength symmetry.MethodsA total of 38 female and 51 male participants were assessed during early (3–6 months post-operative) and late (7–12 months post-operative) phases of rehabilitation following ACLR. Maximal (concentric and isometric peak torque) and explosive (isometric RTD) hamstring and quadriceps strength were assessed and presented as limb symmetry index (LSI).ResultsMaximal concentric hamstrings asymmetry (Early: 86 ± 14; Late 92 ± 13; p = 0.005) as well as maximal concentric (Early, 73 ± 15; Late 91 ± 12; p < 0.001) and explosive (Early: 82 ± 30; Late: 92 ± 25; p = 0.03) quadriceps asymmetry decreased from early to late rehabilitation. However, there were no significant changes in maximal isometric quadriceps strength and explosive isometric hamstring strength in the same time period. Females had a larger asymmetry in maximal concentric (Females: 75 ± 17; Males: 81 ± 15; p = 0.001) and explosive (Females: 81 ± 32; Males: 89 ± 25; p = 0.01) quadriceps strength than males throughout rehabilitation. There were no sex differences in maximal and explosive hamstring strength. There were no sex by time interactions for any variables.ConclusionExplosive hamstring strength asymmetry did not improve despite recovery of maximal hamstring strength during rehabilitation following ACLR with HT autografts. While sex did not influence strength recovery, females had larger maximal and explosive quadriceps strength asymmetry compared to males throughout rehabilitation following ACLR.Level of evidenceLevel III

Poor Accuracy of Intraoperation Medial Proximal Tibial Angle Measurement Compared to Alignment Rod Methods in Open-Wedge High Tibial Osteotomy for Medial Knee Osteoarthritis.

The alignment rod is widely used as an index for intraoperative alignment but alignment error is inevitable. The purpose of this study was to verify the accuracy of lower limb alignment correction by measurement of mechanical medial proximal tibial angle (MPTA) as an index in open-wedge high tibial osteotomy (OWHTO). This study was retrospective case series. This study involved 152 patients undergoing OWHTO for primary medial osteoarthritis. Alignment rod or MPTA measurement board was used as an index of optimal correction in OWHTO. Alignment rod was used from October 2013 to May 2017, and MPTA measurement board was used from June 2017 to April 2020. The correction using an alignment rod was that the weight-bearing line ratio (WBLR) passed through 62.5% of the tibial plateau which was defined as Fujisawa's point under intraoperative fluoroscopy (A rod group). The correction using MPTA measurement board was aligning the intraoperative MPTA to the preplanned angle (MPTA group). Preplanned optimal alignment was defined as Fujisawa's point in all patients. Knee injury and osteoarthritis outcome measure (KOOS), Knee Society scoring system objective knee score (KSS), 3-m timed up-and-go test (TUG), single-limb standing test (SLS), and isometric muscle strength of quadriceps and hamstrings were assessed as clinical results. WBLR, MPTA, joint-line convergence angle (JLCA), and joint-line obliquity (JLO) were assessed as radiological results preoperatively and at 1 year after surgery. The clinical and radiological results after OWHTO were compared with both groups. Postoperative WBLR in A rod group was closer to the target alignment (Fujisawa's point: 62.5) than in the MPTA group at all stage (A rod group vs. MPTA group: 63.1 vs. 54.6 at 6 months; 62.0 vs. 53.4 at 1 year; p < 0.001). There were no significant differences in the clinical results between both groups. The intraoperative measurement of medial proximal tibial angle has a risk of undercorrection after OWHTO. His study is a retrospective case series and reflects level of evidence IV.

Influence of pain quality on physical performance in subjects with osteoarthritis of knee

Objectives Neuropathic pain features are frequently observed in subjects with knee osteoarthritis, which reduces their physical performance. This study was done to compare the physical performance between the subjects with neuropathic and nociceptive pain features. In addition, to assess the relationship between pain quality and physical performance in subjects with osteoarthritis of the knee. Methods Eighty subjects, ranging from 40 − 70 years of both genders with symptomatic and radiologically verified unilateral knee osteoarthritis (OA) were included for the study. Before having them in the study, all the subjects completed baseline interviews and demographic data. The subjects were categorized under neuropathic and nociceptive groups using Pain Detect Questionnaire (PDQ). One-time measurement of pain intensity, isometric strength of Quadriceps & hamstrings, and knee joint range of motion were assessed in both groups. Physical performance was measured using Osteoarthritis Research Society International recommended physical performance tests for knee osteoarthritis (40 m Fast Paced Walk Test, 6 min walk test, 30 s chair stand test, Timed up and Go Test, Stair Climb Test) and OA knee-related disability using Knee injury and Osteoarthritis Outcome Score (KOOS) questionnaire. Results Of the eighty subjects, forty subjects were included in the neuropathic group (44%), forty in the nociceptive group based on PDQ. Physical performance (p < 0.05) was significantly reduced in the neuropathic group. There existed a weak negative correlation between pain quality and variables measured (p < 0.05). Conclusion Physical performance was significantly reduced in OA knee subjects with neuropathic pain features. There is a negative correlation between pain quality and most of the physical performance variables.

Proximal hamstring tendon avulsions: comparable clinical outcomes of operative and non-operative treatment at 1-year follow-up using a shared decision-making model

ObjectiveTo prospectively evaluate 1-year clinical and radiological outcomes after operative and non-operative treatment of proximal hamstring tendon avulsions.MethodsPatients with an MRI-confirmed proximal hamstring tendon avulsion were included. Operative or non-operative...

Effects of Consecutive Matches on Isometric Hamstring Strength, Flexibility Values and Neuromuscular Performance in Female Field Hockey Players. A Prospective, Observational Study

This study aimed to analyze the effects of match congestion in a short period on isometric hamstring strength and hip/ankle range of motion in female field hockey players. Fourteen professional female field hockey players (age: 20.0 ± 5.4 years) played two consecutive hockey matches in 24 h and maximal isometric hamstring strength and hip and ankle range of motion were obtained before and after the first match, after the second match, and 48 h after the second match. Furthermore, locomotion patterns and ratings of perceived exertion were recorded during hockey competitions. Isometric knee flexion strength showed significantly higher values 48 h after the second match for the non-dominant limb (p ≤ 0.005, ηp2 = 0.19), while no differences were reported in the dominant limb (p = 0.370, ηp2 = 0.05). In addition, no differences were reported in the range-of-motion (ROM) variables such as the straight leg raise test or ankle dorsiflexion test (p = 0.075–0.217, ηp2 = 0.01–0.03). The countermovement jump height steadily increased over the matches except between post-match 2 and 48 h after post-match 2 (p &lt; 0.001, η2 = 0.382). Two consecutive official league field hockey matches played within 24 h did not have a negative effect on lower-limb risk factors (strength, hip and ankle ranges of motion, and ratings of perceived exertion) in female field hockey players directly, but they improved 48 h after the matches. This could indicate that 48 h recovery period following matches might be ideal for female field hockey players.

The Influence of Active Hamstring Stiffness on Markers of Isotonic Muscle Performance.

Background: Previous research demonstrates hamstring muscle-tendon stiffness (HMTS) influences isometric strength, landing biomechanics and architectural tissue properties. However, the influence on kinetics & kinematics during other modes of strength testing (isotonic dynamometry) has yet to be established. Purpose: Investigate how HMTS influences kinetics and kinematics during a novel isotonic muscle performance test which has never been done for the hamstrings. Previous work using dynamometry has been limited to isometric or isokinetic contractions, so the novelty arises from our custom isotonic protocol which allows quantitative assessment of the stretch-shortening cycle. Methods: Twenty-six recreationally active individuals (15 males, 11 females, 23.8 ± 2.5 years) completed baseline testing for anthropometry and maximum isometric hamstring strength (MVIC). At least 48 h later, subjects completed a measure of HMTS (damped oscillation technique) followed by an isotonic knee flexion test (eccentric velocity 180°/s; concentric torque 25% of MVIC). Separate linear regression models with examination of residuals were conducted between HMTS and each muscle performance variable. Standardized coefficients determined the magnitude of the relationships. Results: Significance was found for all outcome variables tested. HMTS and rate of torque development demonstrated the strongest relationship followed by isotonic concentric peak torque. The weakest relationship observed was with isometric peak torque. Conclusions: These findings build off previous work quantifying HMTS by showing HMTS more strongly relates to dynamic versus static muscle testing and identifies the potential clinical utility of isotonic dynamometry.

Adolescent Patients Exhibit Significant Improvements in Strength and Functional Performance From 6 to 9 Months After ACL Reconstruction With Quadriceps Autograft

PurposeTo investigate differences between the 6-month and 9-month return to sport (RTS) assessments in adolescent patients undergoing anterior cruciate ligament reconstruction (ACLR) with quadriceps tendon autograft.MethodsA retrospective review was performed of consecutive adolescent patients who underwent ACLR between June 2017 and October 2019. Patients completed a structured RTS test 6 and 9 months after surgery consisting of isometric and isokinetic strength testing, the Lower Quarter Y-Balance Test, and single-legged hop testing. The recovery of muscle strength, assessed via isometric/isokinetic and hop testing, was defined by a limb symmetry index (LSI) ≥90%. Differences were compared between the 2 RTS test time points.ResultsIn total, 27 patients (16 female, 11 male) were identified with a mean age of 15 years (range, 13-17 years). There were statistically significant improvements in isometric quadriceps strength (LSI, 85.0 ± 17.2 vs 92.5 ± 11.3; P = .04) and hamstring strength (LSI, 87.9 ± 11.2 vs 99.0 ± 10.5; P < .01). There were improvements in isokinetic knee extension at both 60°/s (LSI, 75.2 ± 16.7 vs 83.3 ± 13.8) and 180°/s (LSI, 79.9 ± 15.4 vs 83.4 ± 11.2), but the differences were only statistically significant at 60°/s (P = .02 and P = .17, respectively). There were no significant differences in isokinetic testing of knee flexion at either 60°/s or 180°/s. There were no statistically significant differences in the anterior reach component of the Lower Quarter Y-Balance Test at 6 and 9 months. Patients demonstrated statistically significant improvements on single- legged hop testing with mean LSIs >95% for each of the 4 tests at 9 months postop.ConclusionsAdolescent patients undergoing ACLR with quadriceps tendon autograft demonstrated significant improvements in quadriceps strength between 6 and 9 months postoperatively.Level of EvidenceLevel IV, therapeutic case series.

Maximal Isometric or Eccentric Hamstring Strength—Which Test Modality Might Be More Suitable for Assessments in Youth Alpine Ski Racers?

Background: Physical fitness is an important component in the development of youth alpine ski racers. To write systematically planned and age-appropriate fitness programs athletes need to be physically tested at regular intervals at an early age. Although well-developed hamstring muscle strength is important for alpine ski racing performance and the prevention of serious knee injuries, it has not been well investigated, especially in youth athletes. Accordingly, the first aim of the present study was to assess the test-retest reliability of the maximum bilateral eccentric (MBEHS) and unilateral isometric (MUIHS) hamstring tests. The second aim of the present study was to assess whether the results of these two methods correlate and if it is possible to commit to one of the two methods to provide an economic test procedure. Methods: The first study included 26 (14 females/12 males) youth alpine ski racers aged between 12 and 13 years. All athletes performed two MBEHS and two MUIHS tests, 7 days apart. The intraclass correlation coefficient (ICC 3,1) and their 95% confidence intervals based on a consistency two-way mixed model were used to estimate the reliability of the two different test modalities. The second study included 61 (27 females/34 males) youth alpine ski racers aged between 10 and 13 years. All athletes performed one MBEHS and one MUIHS test. Bland-Altman plots and the 95% limits of agreement as well as correlations by Pearson (r) between the different test modalities were assessed. Results: In study 1 “poor” to “moderate” (MBEHS right leg 0.79 (0.58–0.90); left leg 0.83 (0.66–0.92); MUIHS right leg 0.78 (0.56–0.89); left leg 0.66 (0.37–0.83)) ICC values and 95% confident intervals were obtained. Standard error of measurement (SEM) between trails was between 18.3 and 25.1 N. Smallest detectable difference (SDD) was between 50.8 and 69.5 N. In study 2 mean differences between MBEHS and MUIHS was around 20 N with higher values for MBEHS. Significant moderate-to-strong correlations were found between the test modalities (r = 0.74–0.84, p <0.001). Conclusions: The MBEHS test has higher ICC values, lower CV values, higher SEM values and lower SDD values than the MUIHS test. All this suggests that the MBEHS test is more suitable than the MUIHS test to determine the maximum hamstring force in young alpine ski racers.

Unilateral Plyometric Training is Superior to Volume-Matched Bilateral Training for Improving Strength, Speed and Power of Lower Limbs in Preadolescent Soccer Athletes.

This study compared the effects of unilateral and bilateral plyometric training on strength, sprint performance and lower limb power. Sixty-eight preadolescent soccer athletes were randomly assigned to a unilateral plyometric training group (n=23), a bilateral plyometric training group (n=23) and a control group (n=22). Both plyometric training groups trained with equal volumes of unilateral or bilateral exercises for 15 minutes in each session, at which time the control group performed soccer-specific drills. Plyometric exercises were executed twice weekly for 10 weeks during the competitive season. The following tests were performed before and after the intervention: single-leg and double-leg countermovement jump, squat jump, horizontal jumps in different directions, maximal isometric strength of quadriceps and hamstrings, sprint performance, agility and balance. Unilateral plyometric training resulted in greater improvements compared to the control group in the following variables: hamstrings strength (ES: 0.91, p=0.037), 5m sprint time (ES: 0.93, p=0.004), single-leg countermovement jump (ES: 0.90, p=0.006), single- and double-leg squat jump (ES: 0.87, p=0.030 and ES: 0.73, p=0.067, respectively) and single-leg hop performance (ES: 1.01, p=0.004). The only tests where there was an improvement of BPT compared with the CG were the single-leg and double leg SJ (ES: 0.76, p=0.026; ES: 0.70, p=0.050). Quadriceps strength, side hop test, double-leg horizontal jump test, flamingo balance test and modified agility T-test were equally improved in all three groups (p<0.001). In conclusion, unilateral lower-limb plyometric training is more effective in increasing muscle strength and power in preadolescent soccer players when compared to bilateral training or soccer training alone.

6- VS 9-MONTH RETURN TO SPORT TESTING RESULTS AFTER ACL RECONSTRUCTION WITH QUADRICEPS AUTOGRAFT IN ADOLESCENT PATIENTS

Background:Recently, anterior cruciate ligament reconstruction (ACLR) using quadriceps tendon autograft has gained in popularity, particularly in adolescent patients. Studies are lacking that evaluate return to sport (RTS) testing after ACLR with quadriceps tendon autograft (QT).Hypothesis/Purpose:To investigate differences between the 6-month and 9-month RTS assessment in adolescent patients undergoing ACLR with QT.Methods:A retrospective review of adolescent patients who underwent primary ACLR with all soft-tissue QT identified 18 patients with formal RTS testing data at 6 and 9 months. Surgeries were performed between June 2017 and October 2018 by single surgeon using an all-inside technique. Concomitant meniscus repairs were performed in 38.9% of patients. All patients followed the same standardized rehabilitation protocol and completed a structured RTS test 6 and 9 months after surgery. The RTS test consisted of isometric and isokinetic strength testing, the Lower Quarter Y-Balance Test (YBT-LQ), and single-legged hop testing. The recovery of muscle strength, assessed via isometric/isokinetic and hop testing, was defined by a limb symmetry index (LSI) ≥ 90%. Differences were compared between the two RTS time points.Results:The mean age at the time of surgery was 15.2 years (range, 13-17 years). There were statistically significant improvements in the Pedi-IKDC (92.1 ± 8.4 vs. 82.9 ± 8.7; P = 0.001) and Tegner activity scale (7.1 ± 2 vs. 5.1 ± 2; P = 0.001). There were statistically significant improvements in isometric quadriceps strength (LSI, 82.6 ± 16.8 vs. 93.1 ± 11; P = 0.03) and hamstring strength (LSI, 86.4 ± 11.3 vs. 98.2 ± 9.6; P = 0.001). There were improvements in isokinetic knee extension at both 60 deg/sec (LSI, 75 ± 16.9 vs. 82.8 ± 13.9) and 180 deg/sec (LSI, 79.1 ± 14.8 vs. 84.6 ± 10.9), but the differences were not statistically significant (P = 0.08 and P = 0.11, respectively). There were no significant differences in isokinetic testing of knee flexion at either 60 deg/sec or 180 deg/sec. There were no statistically significant differences in the anterior reach component of the YBT-LQ at 6 and 9 months. Patients demonstrated statistically significant improvements on single-legged hop testing with mean LSIs > 95% for each of the four tests at 9 months postop.Conclusion:Adolescent patients undergoing ACLR with QT demonstrated significant improvements in subjective function and quadriceps strength between 6 and 9 months postop. This data supports delaying RTS beyond 9 months in this at-risk population.Table 1.Patient Reported Outcomes and RTS Test Results 6 Months 9 Months P* Pedi-IKDC82.9 ± 8.792.1 ± 8.40.001*Lysholm93.4 ± 6.897.2 ± 3.70.075Tegner5.1 ± 27.1 ± 20.001*Isometric-Q (LSI)82.6 ± 16.893.1 ± 110.03*Isometric-HS (LSI)86.4 ± 11.398.2 ± 9.60.001*Isometric-Hip (LSI)104.9 ± 11.1105.4 ± 7.90.74Isokinetic-Q60 (LSI)75 ± 16.982.8 ± 13.90.08Isokinetic-HS60 (LSI)105.5 ± 20.9104.4 ± 24.80.33Isokinetic-Q180 (LSI)79.1 ± 14.884.6 ± 10.90.11Isokinetic-HS180 (LSI)97.9 ± 20.594.7 ± 15.20.7YBT-LQ Anterior Reach (cm)3.8 ± 52.3 ± 3.20.06Single Hop (LSI)90.1 ± 11.695.1 ± 5.70.01*Triple Hop (LSI)90.3 ± 8.296.6 ± 4.10.01*Crossover Hop (LSI)92.9 ± 13.297.3 ± 3.20.01*Timed Hop (LSI)95.7 ± 10.998.4 ± 5.60.01**statistically significant (P < 0.05)Data reported as mean ± SDRTS, Return to Sport; Q, Quadriceps; HS, Hamstring; LSI, Limb Symmetry Index; YBT-LQ, Lower Quarter Y-Balance Test