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.

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.

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.

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.

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 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.

Microdosing, in the context of resistance training, has increased in popularity within sporting environments where it is frequently used among strength and conditioning professionals. Although there is a clear definition for the concept within the literature, it is still commonly incorrectly used, and the extent to which microdosing has been explicitly investigated in empirical research is limited. However, there are many related research areas or themes (including programming for acute and chronic responses, programming around competition schedules, motor learning, and individualization) that indicate the potential benefits of microdosing as an overarching concept. There are also misinterpretations about the term and what microdosing entails; for example, the term microdosing is often used interchangeably with the concept of the minimum effective dose. Therefore, the aim of this review is to outline and discuss where some of these theories and concepts may or may not be appropriate for use within team sports, while also highlighting areas in which the application of microdosing requires further investigation. Although microdosing may be a relatively new term, which is considered “trendy” among practitioners, the underlying principles associated with microdosing have been expressed and investigated for a long time.