Effect of additional Nordic hamstring exercise or sprint training on the modifiable risk factors of hamstring strain injuries and performance.

The Nordic hamstring exercise (NHE) has commonly been investigated in isolation, however, within practice multiple modalities are commonly incorporated. However, the NHE has a low level of compliance within sport, with sprinting being potentially being preferred. The present study aimed to observe the effect of a lower-limb program with either additional NHE or sprinting on the modifiable risk factors hamstring strain injury (HSI) and athletic performance. 38 collegiate athletes were randomly assigned into three groups: control standardised lower-limb training program (n = 10 (2 female, 8 male), age = 23.50 ± 2.95 years, height = 1.75 ± 0.09 m, mass 77.66 ± 11.82 kg), additional NHE (n = 15 (7 female, 8 male), age = 21.40 ± 2.64 years, height = 1.74 ± 0.04 m, mass 76.95 ± 14.20 kg) and additional sprinting (n = 13 (4 female, 9 male), age = 22.15 ± 2.54 years, height = 1.74 ± 0.05 m, mass 70.55 ± 7.84 kg). All participants performed a standardised lower-limb training program twice per week for seven weeks, including Olympic lifting derivatives, squatting movements, and the Romanian deadlift, with experimental groups performing with either additional sprinting or NHE. Bicep femoris architecture, eccentric hamstring strength, jump performance, lower-limb maximal strength and sprint ability were measured pre and post. All training groups demonstrated significant (p < 0.001), small-moderate increases in Bicep femoris architecture (g = 0.60-1.22), with significant (p < 0.001), small-large increases in absolute and relative eccentric peak force (g = 0.60-1.84). Significant and small increases were observed in take-off velocity and mean propulsion force (p < 0.02, g = 0.47-0.64), with non-significant and small increases for both the sprint and control training groups for mean propulsion force (p > 0.05, g = 0.42-0.50). Nordic and sprint training groups had significant and small increases in peak absolute and relative net force (p < 0.001, g = 0.44-0.60). The control group had a non-significant trivial increase in absolute peak net force (p > 0.05, g = 0.22), with a significant and small increase in relative peak relative net force (p = 0.034, g = 0.48). Significant and small decreases for the NHE and sprinting training groups was observed for 0-10 m, 0-20 m, and 10-20 m sprint time (p < 0.010, g = 0.47-0.71). Performing multiple modalities, with either additional NHE or sprinting, as part of a complete resistance training program was superiorly effective for measures of modifiable risk factors HSI, with similar increases observed in measures of athletic performance derived from the standardised lower-limb training program.

The Effect of Exercise Compliance on Risk Reduction for Hamstring Strain Injury: A Systematic Review and Meta-Analyses.

Eccentric strength training can reduce the risk of hamstring strain injury (HSI) occurrence; however, its implementation can be impacted by athlete compliance and prescription. The aim of this review was to investigate the effects of intervention compliance, consistency and modality, on the prevention of HSIs among athletes. A literature search was conducted. 868 studies were identified prior to the application of the exclusion criteria which resulted in 13 studies identified. Random effects models were used to produce log odds ratios and 95% confidence intervals. Very high (>75.1%), moderate-high (50.1-75%), low-moderate (25.1-50%) and very low (<25%) and <1-, 1.01-3.00-, >3.01-weeks/session were used as thresholds of compliance and consistency, respectively. Modality was also observed. A positive effect on HSI incidence -0.61 (-1.05 to -0.17), favoring the intervention treatments (Z = -2.70, p = 0.007). There were non-significant, large differences between compliance (p = 0.203, Z = -1.272) and consistency (p = 0.137, Z = -1.488), with increased compliance and consistency showing greater effectiveness. A significant difference between intervention modalities was observed (p < 0.001, Z = -4.136), with eccentric interventions being superiorly effective. Compliance of >50.1% and consistent application with <3 weeks/session having positive effects on HSI incidence. Training interventions that can achieve high levels of compliance, and can be consistently performed, should be the objective of future practice.

Effects of Spaceflight on Musculoskeletal Health: A Systematic Review and Meta-analysis, Considerations for Interplanetary Travel.

BACKGROUND: If interplanetary travel is to be successful over the coming decades, it is essential that countermeasures to minimize deterioration of the musculoskeletal system are as effective as possible, given the increased duration of spaceflight associated with such missions. The aim of this review, therefore, is to determine the magnitude of deconditioning of the musculoskeletal system during prolonged spaceflight and recommend possible methods to enhance the existing countermeasures. METHODS: A literature search was conducted using PubMed, Ovid and Scopus databases. 5541 studies were identified prior to the removal of duplicates and the application of the following inclusion criteria: (1) group means and standard deviations for pre- and post-spaceflight for measures of strength, muscle mass or bone density were reported (or provided by the corresponding author when requested via e-mail), (2) exercise-based countermeasures were included, (3) the population of the studies were human, (4) muscle function was assessed and (5) spaceflight rather than simulated spaceflight was used. The methodological quality of the included studies was evaluated using a modified Physiotherapy Evidence Database (PEDro) scale for quality, with publication bias assessed using a failsafe N (Rosenthal method), and consistency of studies analysed using I2 as a test of heterogeneity. Secondary analysis of studies included Hedges' g effect sizes, and between-study differences were estimated using a random-effects model. RESULTS: A total of 11 studies were included in the meta-analyses. Heterogeneity of the completed meta-analyses was conducted revealing homogeneity for bone mineral density (BMD) and spinal muscle size (Tau2 < 0.001; I2 = 0.00%, p > 0.05), although a high level of heterogeneity was noted for lower body force production (Tau2 = 1.546; I2 = 76.03%, p < 0.001) and lower body muscle mass (Tau2 = 1.386; I2 = 74.38%, p < 0.001). The estimated variance (≤ -0.306) for each of the meta-analyses was significant (p ≤ 0.033), for BMD (- 0.48 to - 0.53, p < 0.001), lower body force production (- 1.75, p < 0.001) and lower body muscle size (- 1.98, p < 0.001). Spaceflight results in small reductions in BMD of the femur (Hedges g = - 0.49 [- 0.69 to - 0.28]), trochanter (Hedges g = - 0.53 [- 0.77 to - 0.29]), and lumbo-pelvic region (Hedges g = - 0.48 [- 0.73 to - 0.23]), but large decreases in lower limb force production (Hedges g = - 1.75 [- 2.50 to - 0.99]) and lower limb muscle size (Hedges g = - 1.98 [- 2.72 to - 1.23]). CONCLUSIONS: Current exercise countermeasures result in small reductions in BMD during long-duration spaceflight. In contrast, such exercise protocols do not alleviate the reductions in muscle function or muscle size, which may be attributable to the low to moderate loads reported by crewmembers and the interference effect associated with concurrent training. It is recommended that higher-load resistance exercise and the use of high-intensity interval training should be investigated, to determine if such modifications to the reported training practices result in more effective countermeasures to the deleterious effect of long-duration spaceflight on the muscular system.

Electromyographical Differences Between the Hyperextension and Reverse-Hyperextension.

ABSTRACT: Cuthbert, M, Ripley, NJ, Suchomel, TJ, Alejo, R, McMahon, JJ, and Comfort, P. Electromyographical differences between the hyperextension and reverse-hyperextension. J Strength Cond Res 35(6): 1477-1483, 2021-The aims of this study were to compare muscle activation of the erector spinae (ES), gluteus maximus (GMax), and biceps femoris (BF) during the hyperextension (HE) and reverse-HE (RHE) exercises. Ten subjects (age, 23 ± 4 years; height, 175.9 ± 6.9 cm; mass, 75.2 ± 9.7 kg) had electromyography (EMG) electrodes placed on the ES, GMax, and BF muscles in accordance with SENIAM (Surface EMG for Non-Invasive Assessment of Muscles) guidelines. Subjects performed 3 maximum voluntary isometric contraction trials of lumbar extension and hip extension using a handheld and isokinetic dynamometer, respectively, to normalize the EMG during the HE and RHE exercises. Three repetitions of each exercise were executed in a randomized order. High reliability (intraclass correlation coefficient ≥0.925) was observed with low variability (coefficient of variation [CV] < 10%) in all but the GMax during the extension phase of the HE (CV = 10.64%). During the extension and flexion phases, the RHE exhibited significantly greater (p ≤ 0.024; 34.1-70.7% difference) peak EMG compared with the HE in all muscles tested. Similarly, the RHE resulted in significantly greater mean EMG compared with the HE (p ≤ 0.036; 28.2-65.0% difference) in all muscles except the BF during the flexion phase (p = 9.960). Therefore, the RHE could be considered as a higher-intensity exercise for the posterior chain muscles compared with the HE, potentially eliciting greater increases in strength of the posterior chain muscles.

Effects of Variations in Resistance Training Frequency on Strength Development in Well-Trained Populations and Implications for In-Season Athlete Training: A Systematic Review and Meta-analysis.

BACKGROUND: In-season competition and tournaments for team sports can be both long and congested, with some sports competing up to three times per week. During these periods of time, athletes need to prepare technically, tactically and physically for the next fixture and the short duration between fixtures means that, in some cases, physical preparation ceases, or training focus moves to recovery as opposed to progressing adaptations. OBJECTIVE: The aim of this review was to investigate the effect of training frequency on muscular strength to determine if a potential method to accommodate in-season resistance training, during busy training schedules, could be achieved by utilizing shorter more frequent training sessions across a training week. METHODS: A literature search was conducted using the SPORTDiscus, Ovid, PubMed and Scopus databases. 2134 studies were identified prior to application of the following inclusion criteria: (1) maximal strength was assessed, (2) a minimum of two different training frequency groups were included, (3) participants were well trained, and finally (4) compound exercises were included within the training programmes. A Cochrane risk of bias assessment was applied to studies that performed randomized controlled trials and consistency of studies was analysed using I2 as a test of heterogeneity. Secondary analysis of studies included Hedges' g effect sizes (g) and between-study differences were estimated using a random-effects model. RESULTS: Inconsistency of effects between pre- and post-intervention was low within-group (I2 = 0%), and moderate between-group (I2 ≤ 73.95%). Risk of bias was also low based upon the Cochrane risk of bias assessment. Significant increases were observed overall for both upper (p ≤ 0.022) and lower (p ≤ 0.008) body strength, pre- to post-intervention, when all frequencies were assessed. A small effect was observed between training frequencies for upper (g ≤ 0.58) and lower body (g ≤ 0.45). CONCLUSION: Over a 6-12-week period, there are no clear differences in maximal strength development between training frequencies, in well-trained populations. Such observations may permit the potential for training to be manipulated around competition schedules and volume to be distributed across shorter, but more frequent training sessions within a micro-cycle rather than being condensed into 1-2 sessions per week, in effect, allowing for a micro-dosing of the strength stimuli.

Unilateral vs. bilateral hamstring strength assessments: comparing reliability and inter-limb asymmetries in female soccer players.

The aims in the present study were to assess reliability for two unilateral and two bilateral field-based hamstring assessments and compare magnitude, direction and agreement of inter-limb asymmetry between tests and sessions. Twenty-nine female soccer players (age: 21.1 ± 4.5 years; height: 169.7 ± 5.8 cm; body mass: 66.2 ± 6.4 kg) performed three repetitions per leg of unilateral isometric 30° and 90° knee flexion (KF) tasks, and three repetitions total for a bilateral 90° isometric KF and Nordic hamstring exercise. Absolute reliability of most methods were acceptable (<10%). Relative reliability within-session was fair to excellent (ICC≥0.784; lower bound 95%CI ≥0.623). Greater variability in between-session relative reliability was observed during the unilateral tests, demonstrating poor to good (ICC = 0.698-0.798; lower bound 95%CI = 0.274-0.638). Bilateral assessments demonstrated similar ranges of poor to excellent (ICC = 0.679-0.963; lower bound 95%CI = 0.231-0.790). Agreement between-session for inter-limb asymmetry identification was slight and fair in the unilateral tests, with moderate to substantial agreement demonstrated in the bilateral. Being the most reliable within- and between-sessions, demonstrating substantial agreement in asymmetry between-sessions, the NHE would be most appropriate to identify inter-limb asymmetry and assess chronic changes in hamstring strength.

The Effect of Nordic Hamstring Exercise Intervention Volume on Eccentric Strength and Muscle Architecture Adaptations: A Systematic Review and Meta-analyses.

BACKGROUND: Although performance of the Nordic hamstring exercise (NHE) has been shown to elicit adaptations that may reduce hamstring strain injury (HSI) risk and occurrence, compliance in NHE interventions in professional soccer teams is low despite a high occurrence of HSI in soccer. A possible reason for low compliance is the high dosages prescribed within the recommended interventions. The aim of this review was to investigate the effect of NHE-training volume on eccentric hamstring strength and biceps femoris fascicle length adaptations. METHODS: A literature search was conducted using the SPORTDiscus, Ovid, and PubMed databases. A total of 293 studies were identified prior to application of the following inclusion criteria: (1) a minimum of 4 weeks of NHE training was completed; (2) mean ± standard deviation (SD) pre- and post-intervention were provided for the measured variables to allow for secondary analysis; and (3) biceps femoris muscle architecture was measured, which resulted in 13 studies identified for further analysis. The TESTEX criteria were used to assess the quality of studies with risk of bias assessment assessed using a fail-safe N (Rosenthal method). Consistency of studies was analysed using I2 as a test of heterogeneity and secondary analysis of studies included Hedges' g effect sizes for strength and muscle architecture variables to provide comparison within studies, between-study differences were estimated using a random-effects model. RESULTS: A range of scores (3-11 out of 15) from the TESTEX criteria were reported, showing variation in study quality. A 'low risk of bias' was observed in the randomized controlled trials included, with no study bias shown for both strength or architecture (N = 250 and 663, respectively; p < 0.001). Study consistency was moderate to high for strength (I2 = 62.49%) and muscle architecture (I2 = 88.03%). Within-study differences showed that following interventions of ≥ 6 weeks, very large positive effect sizes were seen in eccentric strength following both high volume (g = 2.12) and low volume (g = 2.28) NHE interventions. Similar results were reported for changes in fascicle length (g ≥ 2.58) and a large-to-very large positive reduction in pennation angle (g ≥ 1.31). Between-study differences were estimated to be at a magnitude of 0.374 (p = 0.009) for strength and 0.793 (p < 0.001) for architecture. CONCLUSIONS: Reducing NHE volume prescription does not negatively affect adaptations in eccentric strength and muscle architecture when compared with high dose interventions. These findings suggest that lower volumes of NHE may be more appropriate for athletes, with an aim to increase intervention compliance, potentially reducing the risk of HSI.

Corrections to: The Effect of Nordic Hamstring Exercise Intervention Volume on Eccentric Strength and Muscle Architecture Adaptations: A Systematic Review and Meta-analyses.

between the studies assessed for.

Application of Change of Direction Deficit to Evaluate Cutting Ability.

Cuthbert, M, Thomas, C, Dos'Santos, T, and Jones, PA. Application of change of direction deficit to evaluate cutting ability. J Strength Cond Res 33(8): 2138-2144, 2019-The purpose of this study was to examine the application of the change of direction deficit (CODD) to a 90° cut test to examine whether CODD provides a unique evaluation of an individual's cutting ability. Thirty-six male collegiate team-sport (23 Rugby/13 Soccer) athletes (age: 20 ± 1.4 years; height: 1.80 ± 0.08 m; mass: 83 ± 13.2 kg) participated in the study. Each athlete performed 3 trials of a 20-m sprint (with 5 and 10 m splits) and 2 change of direction (COD) tests (90° cut and 505 tests) cutting/turning from both legs. Completion times for all sprint and COD tests were measured using timing cells. For both COD tests, CODD was determined (COD completion time-10 m sprint time). Pearson correlation was used to explore the relationships between sprint times and CODD and completion times. Significant (p < 0.001) moderate-to-large (r ≥ 0.467) correlations between sprint times and 90° cut completion times for left and right cuts were observed. Nonsignificant (p > 0.05) trivial-to-small correlations (r ≤ 0.199) were found between sprint variables and 90° cut CODD. Significant (p < 0.001) large to very large correlations (r ≥ 0.531) were revealed between the left and right 90° cut and 90° cut CODD. The results suggest that the CODD could be applied to isolate and assess the cutting ability in COD speed tests that involve a single cutting maneuver. Failure to inspect CODD could lead to incorrect evaluation of an athletes cutting or COD ability.