Nirav Maniar

Architectural Changes of the Biceps Femoris Long Head after Concentric or Eccentric Training.

PURPOSE To determine the architectural adaptations of the biceps femoris long head (BFlh) after concentric or eccentric strength training interventions and the time course of adaptation during training and detraining. METHODS Participants in this intervention (concentric training group [n = 14], eccentric training group [n = 14], male subjects) completed a 4-wk control period, followed by 6 wk of either concentric- or eccentric-only knee flexor training on an isokinetic dynamometer and finished with 28 d of detraining. Architectural characteristics of BFlh were assessed at rest and during graded isometric contractions using two-dimensional ultrasonography at 28 d prebaseline; baseline; and days 14, 21, and 42 of the intervention and then again after 28 d of detraining. RESULTS BFlh fascicle length was significantly longer in the eccentric training group (P < 0.05; d range, 2.65-2.98) and shorter in the concentric training group (P < 0.05; d range, -1.62 to -0.96) after 42 d of training compared with baseline at all isometric contraction intensities. After the 28-d detraining period, BFlh fascicle length was significantly reduced in the eccentric training group at all contraction intensities compared with the end of the intervention (P < 0.05; d range, -1.73 to -1.55). There was no significant change in fascicle length of the concentric training group after the detraining period. CONCLUSIONS These results provide evidence that short-term resistance training can lead to architectural alterations in the BFlh. In addition, the eccentric training-induced lengthening of BFlh fascicle length was reversed and returned to baseline values after 28 d of detraining. The contraction mode specific adaptations in this study may have implications for injury prevention and rehabilitation.

Hamstring strength and flexibility after hamstring strain injury: a systematic review and meta-analysis

Objective To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings. Design Systematic review and meta-analysis. Data sources A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015. Inclusion criteria Full-text English articles which included studies which assessed at least one measure of hamstring strength or flexibility in men and women with prior hamstring strain injury within 24 months of the testing date. Results Twenty-eight studies were included in the review. Previously injured legs demonstrated deficits across several variables. Lower isometric strength was found <7 days postinjury (d=−1.72), but this did not persist beyond 7 days after injury. The passive straight leg raise was restricted at multiple time points after injury (<10 days, d=−1.12; 10–20 days, d=−0.74; 20–30 days, d=−0.40), but not after 40–50 days postinjury. Deficits remained after return to play in isokinetically measured concentric (60°/s, d=−0.33) and Nordic eccentric knee flexor strength (d=−0.39). The conventional hamstring to quadricep strength ratios were also reduced well after return to play (60:60°/s, d=−0.32; 240:240°/s, d=−0.43) and functional (30:240°/s, d=−0.88), but these effects were inconsistent across measurement methods. Conclusions After hamstring strain, acute isometric and passive straight leg raise deficits resolve within 20–50 days. Deficits in eccentric and concentric strength and strength ratios persist after return to play, but this effect was inconsistent across measurement methods. Flexibility and isometric strength should be monitored throughout rehabilitation, but dynamic strength should be assessed at and following return to play.

Non-knee-spanning muscles contribute to tibiofemoral shear as well as valgus and rotational joint reaction moments during unanticipated sidestep cutting

Anterior cruciate ligament (ACL) injuries are a burdensome condition due to potential surgical requirements and increased risk of long term debilitation. Previous studies indicate that muscle forces play an important role in the development of ligamentous loading, yet these studies have typically used cadaveric models considering only the knee-spanning quadriceps, hamstrings and gastrocnemius muscle groups. Using a musculoskeletal modelling approach, we investigated how lower-limb muscles produce and oppose key tibiofemoral reaction forces and moments during the weight acceptance phase of unanticipated sidestep cutting. Muscles capable of opposing (or controlling the magnitude of) the anterior shear force and the external valgus moment at the knee are thought to be have the greatest potential for protecting the anterior cruciate ligament from injury. We found the best muscles for generating posterior shear to be the soleus, biceps femoris long head and medial hamstrings, providing up to 173N, 111N and 77N of force directly opposing the anterior shear force. The valgus moment was primarily opposed by the gluteus medius, gluteus maximus and piriformis, with these muscles providing contributions of up to 32 Nm, 19 Nm and 21 Nm towards a knee varus moment, respectively. Our findings highlight key muscle targets for ACL preventative and rehabilitative interventions.

A Novel Apparatus to Measure Knee Flexor Strength During Various Hamstring Exercises: A Reliability and Retrospective Injury Study

• STUDY DESIGN: Reliability and case‐control injury study. • BACKGROUND: Knee flexor strength is a key variable when dealing with hamstring strain injury (HSI), and methodologies of objective measurement of strength are often limited to single exercises. • OBJECTIVES: To establish test‐retest reliability of a novel apparatus to measure knee flexor strength during various hamstring exercises, and to investigate whether the measure can detect between‐leg differences in male participants with and without history of unilateral HSI. • METHODS: Twenty male participants without and 10 male participants with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0°/0°, 45°/45°, and 90°/90° of hip/knee flexion were measured, as well as force impulse during bilateral and unilateral variations of an eccentric slider and hamstring bridge, using a novel apparatus. Intraclass correlation coefficient (ICC), typical error, and typical error as a coefficient of variation were calculated for all measures. The magnitudes of between‐leg differences within each group were calculated using estimates of effect sizes, reported as Cohens d and 90% confidence interval (CI). • RESULTS: Moderate to high test‐retest reliability was observed for isometric knee flexor strength (ICC = 0.87‐0.92) and peak RFD (ICC = 0.88‐0.95) across 3 positions and for mean force impulse during the eccentric slider (ICC = 0.83‐0.90). In those with prior HSI, large deficits were observed in the previously injured leg compared to the contralateral uninjured leg for mean force impulse during the unilateral eccentric slider (d = ‐1.09; 90% CI: ‐0.20, ‐1.97), isometric strength at 0°/0° (d = ‐1.06; 90% CI: ‐0.18, ‐1.93) and 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74), and peak RFD at 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74). • CONCLUSION: The novel apparatus provides a reliable measure of isometric knee flexor strength, peak RFD, and force impulse during an eccentric slider, with deficits seen in previously injured hamstrings for these measures.

A novel apparatus to measure knee flexor strength during various hamstring exercises: A reliability and retrospective injury study [accepted manuscript]

• STUDY DESIGN: Reliability and case‐control injury study. • BACKGROUND: Knee flexor strength is a key variable when dealing with hamstring strain injury (HSI), and methodologies of objective measurement of strength are often limited to single exercises. • OBJECTIVES: To establish test‐retest reliability of a novel apparatus to measure knee flexor strength during various hamstring exercises, and to investigate whether the measure can detect between‐leg differences in male participants with and without history of unilateral HSI. • METHODS: Twenty male participants without and 10 male participants with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0°/0°, 45°/45°, and 90°/90° of hip/knee flexion were measured, as well as force impulse during bilateral and unilateral variations of an eccentric slider and hamstring bridge, using a novel apparatus. Intraclass correlation coefficient (ICC), typical error, and typical error as a coefficient of variation were calculated for all measures. The magnitudes of between‐leg differences within each group were calculated using estimates of effect sizes, reported as Cohens d and 90% confidence interval (CI). • RESULTS: Moderate to high test‐retest reliability was observed for isometric knee flexor strength (ICC = 0.87‐0.92) and peak RFD (ICC = 0.88‐0.95) across 3 positions and for mean force impulse during the eccentric slider (ICC = 0.83‐0.90). In those with prior HSI, large deficits were observed in the previously injured leg compared to the contralateral uninjured leg for mean force impulse during the unilateral eccentric slider (d = ‐1.09; 90% CI: ‐0.20, ‐1.97), isometric strength at 0°/0° (d = ‐1.06; 90% CI: ‐0.18, ‐1.93) and 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74), and peak RFD at 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74). • CONCLUSION: The novel apparatus provides a reliable measure of isometric knee flexor strength, peak RFD, and force impulse during an eccentric slider, with deficits seen in previously injured hamstrings for these measures.

Lower-limb muscle function during sidestep cutting

To investigate lower-limb muscle function during sidestep cutting, prior studies have analysed electromyography (EMG) data together with three dimensional motion analysis. Such an approach does not directly quantify the biomechanical role of individual lower-limb muscles during a sidestep cut. This study recorded three dimensional motion analysis, ground reaction force (GRF) and EMG data for eight healthy males executing an unanticipated sidestep cut. Using a musculoskeletal modelling approach, muscle function was determined by computing the muscle contributions to the GRFs and lower-limb joint moments. We found that bodyweight support (vertical GRF) was primarily provided by the vasti, gluteus maximus, soleus and gastrocnemius. These same muscles, along with the hamstrings, were also primarily responsible for modulating braking and propulsion (anteroposterior GRF). The vasti, gluteus maximus and gluteus medius were the key muscles for accelerating the centre-of-mass towards the desired cutting direction by generating a medially-directed GRF. Our findings have implications for designing retraining programs to improve sidestep cutting technique.

Effect of Prior Injury on Changes to Biceps Femoris Architecture Across an Afl Season

Purpose To assess in-season alterations of biceps femoris long head (BFlh) fascicle length in elite Australian footballers with and without a history of unilateral hamstring strain injury (HSI) in the past 12 months. Methods Thirty elite Australian football players were recruited. Twelve had a history of unilateral HSI. Eighteen had no HSI history. All had their BFlh architecture assessed at approximately monthly intervals, six times across a competitive season. Results The previously injured limb’s BFlh fascicles increased from the start of the season and peaked at week 5. Fascicle length gradually decreased until the end of the season, where they were shortest. The contralateral uninjured limb’s fascicles were the longest when assessed at week 5 and showed a reduction in-season where weeks 17 and 23 were shorter than week 1. Control group fascicles were longest at week 5 and reduced in-season. The previously injured limb’s BFlh fascicles were shorter than the control group at all weeks and the contralateral uninjured limb at week 5. Compared with the control group, the contralateral uninjured limb had shorter fascicles from weeks 9 to 23. Conclusions Athletes with a history of HSI end the season with shorter fascicles than they start. Limbs without a history of HSI display similar BFlh fascicle lengths at the end of the season as they begin with. All athletes increase fascicle length at the beginning of the season; however, the extent of the increase differed based on history of HSI. These findings show that a HSI history may influence structural adaptation of the BFlh in-season.

Predictive Modeling of Hamstring Strain Injuries in Elite Australian Footballers

Purpose Three of the most commonly identified hamstring strain injury (HSI) risk factors are age, previous HSI, and low levels of eccentric hamstring strength. However, no study has investigated the ability of these risk factors to predict the incidence of HSI in elite Australian footballers. Accordingly, the purpose of this prospective cohort study was to investigate the predictive ability of HSI risk factors using machine learning techniques. Methods Eccentric hamstring strength, demographic and injury history data were collected at the start of preseason for 186 and 176 elite Australian footballers in 2013 and 2015, respectively. Any prospectively occurring HSI were reported to the research team. Using various machine learning techniques, predictive models were built for 2013 and 2015 within-year HSI prediction and between-year HSI prediction (2013 to 2015). The calculated probabilities of HSI were compared with the injury outcomes and area under the curve (AUC) was determined and used to assess the predictive performance of each model. Results The minimum, maximum, and median AUC values for the 2013 models were 0.26, 0.91, and 0.58, respectively. For the 2015 models, the minimum, maximum and median AUC values were, correspondingly, 0.24, 0.92, and 0.57. For the between-year predictive models the minimum, maximum, and median AUC values were 0.37, 0.73, and 0.52, respectively. Conclusions Although some iterations of the models achieved near perfect prediction, the large ranges in AUC highlight the fragility of the data. The 2013 models performed slightly better than the 2015 models. The predictive performance of between-year HSI models was poor however. In conclusion, risk factor data cannot be used to identify athletes at an increased risk of HSI with any consistency.

A Novel Apparatus Measuring Knee Flexor Strength During Various Hamstring Exercises: A Reliability and Retrospective Study

• STUDY DESIGN: Reliability and case‐control injury study. • BACKGROUND: Knee flexor strength is a key variable when dealing with hamstring strain injury (HSI), and methodologies of objective measurement of strength are often limited to single exercises. • OBJECTIVES: To establish test‐retest reliability of a novel apparatus to measure knee flexor strength during various hamstring exercises, and to investigate whether the measure can detect between‐leg differences in male participants with and without history of unilateral HSI. • METHODS: Twenty male participants without and 10 male participants with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0°/0°, 45°/45°, and 90°/90° of hip/knee flexion were measured, as well as force impulse during bilateral and unilateral variations of an eccentric slider and hamstring bridge, using a novel apparatus. Intraclass correlation coefficient (ICC), typical error, and typical error as a coefficient of variation were calculated for all measures. The magnitudes of between‐leg differences within each group were calculated using estimates of effect sizes, reported as Cohens d and 90% confidence interval (CI). • RESULTS: Moderate to high test‐retest reliability was observed for isometric knee flexor strength (ICC = 0.87‐0.92) and peak RFD (ICC = 0.88‐0.95) across 3 positions and for mean force impulse during the eccentric slider (ICC = 0.83‐0.90). In those with prior HSI, large deficits were observed in the previously injured leg compared to the contralateral uninjured leg for mean force impulse during the unilateral eccentric slider (d = ‐1.09; 90% CI: ‐0.20, ‐1.97), isometric strength at 0°/0° (d = ‐1.06; 90% CI: ‐0.18, ‐1.93) and 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74), and peak RFD at 45°/45° (d = ‐0.88; 90% CI: ‐0.02, ‐1.74). • CONCLUSION: The novel apparatus provides a reliable measure of isometric knee flexor strength, peak RFD, and force impulse during an eccentric slider, with deficits seen in previously injured hamstrings for these measures.