Effect of an Isometric or Eccentric Hip Extension Exercise Intervention on Hamstring Strength, Architecture, and Morphology

Establishing the Validity of Low Sampling Rates for Assessing Force/Torque-Time Variables During Isometric Strength Tests

PURPOSE

Skeletal-muscle function is commonly assessed during isometric strength tests for both athletic and clinical populations. To assess neuromuscular performance, these are often analyzed by calculating peak force/torque and rate of force/torque development (RFD/RTD) variables using dynamometers, load cells, or force plates. These devices record a specific number of data points per second, known as the sampling rate, measured in samples per second (in hertz). It is unclear what the validity of sampling rates lower than the recommended 1000 Hz is for practical neuromuscular strength assessments.

METHODS

This study examined the validity of sampling rates below previous recommendations of 1000 Hz for force/torque-time variable analysis. These variables were calculated at low sampling rates for maximal isometric strength tests of knee extension, knee flexion, and midthigh pull. The difference between each variable at 1000-Hz data and down-sampled data at 500, 250, 100, and 50 Hz was evaluated (ie, mean bias).

RESULTS

We obtained 1547 trials of individual repetitions from 4 previously published studies and 1 unpublished study (80 participants in total), with 1451 of these trials eligible for force/torque-time analysis. Mean bias of down-sampled data did not exceed -0.1% for peak force/torque, -2.1% for peak RFD/RTD, and -15.3% for fixed time epoch RFD/RTD variables.

CONCLUSIONS

Practitioners may adopt lower sampling rates into practice for force/torque-time analysis, particularly for variables of peak force/torque or peak RFD/RTD calculations.

Strength effects of the Copenhagen adduction exercise vs an adductor squeeze exercise in male football players - A randomized controlled trial

To examine the effect of assigning male football players to an 8-week Copenhagen Adduction (CA) and Adductor Squeeze (SQ) Pragmatic randomized controlled trial, 57 participants (16.7 ± 0.9 years, 175.9 ± 7.3 height and 66 ± 8.4 weight) were individually randomized to an 8-week progressive dynamic training protocol with the CA or an isometric training protocol with the SQ twice per week. Maximal eccentric (EHAD) and isometric (IHAD) hip adductor torque was tested with a handheld dynamometer. Perceived exertion and delayed onset muscle soreness (DOMS) were recorded throughout the intervention period. In the intention-to-treat analysis, no significant between-group difference was observed for EHAD (p = 0.478-0.833) nor IHAD (p = 0.084-0.118). There was a significant difference in DOMS between groups in the third to sixteenth exercise session, with the CA group reporting higher values (median varying between 0-3 vs 0-1, p = 0.000-0.009). Perceived exertion was greater for the CA group only in the fifteenth exercise session of the protocol (median of 4 vs 3, p = 0.031). No other significant differences between the groups were observed for DOMS nor perceived exertion. An 8-week adductor training program with either the Copenhagen Adduction or Adductor Squeeze exercise performed with two sets twice a week and adjusted for total volume did not result in significant differences in eccentric nor isometric adduction torque between the groups.

Biceps femoris long head muscle and aponeurosis geometry in males with and without a history of hamstring strain injury

OBJECTIVES

Hamstring strain injuries (HSIs) commonly affect the proximal biceps femoris long head (BFlh) musculotendinous junction. Biomechanical modeling suggests narrow proximal BFlh aponeuroses and large muscle-to-aponeurosis width ratios increase localized tissue strains and presumably risk of HSI. This study aimed to determine if BFlh muscle and proximal aponeurosis geometry differed between limbs with and without a history of HSI.

METHODS

Twenty-six recreationally active males with (n = 13) and without (n = 13) a history of unilateral HSI in the last 24 months underwent magnetic resonance imaging of both thighs. BFlh muscle and proximal aponeurosis cross-sectional areas, length, volume, and interface area between muscle and aponeurosis were extracted. Previously injured limbs were compared to uninjured contralateral and control limbs for discrete variables and ratios, and along the relative length of tissues using statistical parametric mapping.

RESULTS

Previously injured limbs displayed significantly smaller muscle-to-aponeurosis volume ratios (p = 0.029, Wilcoxon effect size (ES) = 0.43) and larger proximal BFlh aponeurosis volumes (p = 0.019, ES = 0.46) than control limbs with no history of HSI. No significant differences were found between previously injured and uninjured contralateral limbs for any outcome measure (p = 0.216-1.000, ES = 0.01-0.36).

CONCLUSIONS

Aponeurosis geometry differed between limbs with and without a history of HSI. The significantly larger BFlh proximal aponeuroses and smaller muscle-to-aponeurosis volume ratios in previously injured limbs could alter the strain experienced in muscle adjacent to the musculotendinous junction during active lengthening. Future research is required to determine if geometric differences influence the risk of re-injury and whether they can be altered via targeted training.

The Effect of Eccentric or Isometric Training on Strength, Architecture, and Sprinting across an Australian Football Season

PURPOSE

This study aimed to investigate the effect of an isometric (ISO) or Nordic hamstring exercise (NHE) intervention, alongside a sprint training program on hamstring strength, architecture, and sprinting performance in Australian footballers.

METHODS

Twenty-five male athletes undertook NHE ( n = 13) or ISO ( n = 12) training across a 38-wk period (including preseason and in season). Biceps femoris long head (BFlh) architecture, ISO, and eccentric knee flexor strength were assessed at baseline, at the end of preseason (14 wk), and at the conclusion of the intervention. Sprint times and force-velocity profiles were determined at baseline and at the end of preseason.

RESULTS

After the intervention, both groups had significant improvements in BFlh fascicle length (NHE: 1.16 cm, 95% CI = 0.68 to 1.63 cm, d = 1.88, P < 0.001; ISO: 0.82 cm, 95% CI = 0.57 to 1.06 cm, d = 1.70, P < 0.001), muscle thickness (NHE: 0.11 cm, 95% CI = 0.01 to 0.21 cm, d = 0.51, P = 0.032; ISO: 0.21 cm, 95% CI = 0.10 to 0.32 cm, d = 0.86, P = 0.002), and eccentric strength (NHE: 83 N, 95% CI = 53 to 114 N, d = 1.79, P < 0.001; ISO: 83 N, 95% CI = 17 to 151 N, d = 1.17, P = 0.018). Both groups also finished the intervention weaker isometrically than they started (NHE: -45 N, 95% CI = -81 to -8 N, d = -1.03, P = 0.022; ISO: -80 N, 95% CI = -104 to -56 N, d = -3.35, P < 0.001). At the end of preseason, the NHE group had improved their 5-m sprint time by 3.3% ± 2.0%), and their maximum horizontal velocity was 3% ± 2.1% greater than the ISO group who saw no changes.

CONCLUSIONS

Both ISO and NHE training with a periodized sprinting program can increase BFlh fascicle length, thickness, and eccentric strength in Australian footballers. NHE training also improves 5-m sprint time and maximum velocity. However, both interventions reduced ISO strength. These findings provide unique, contextually relevant insights into the adaptations possible in semiprofessional athletes.

Individual distribution of muscle hypertrophy among hamstring muscle heads: Adding muscle volume where you need is not so simple

PURPOSE

The aim of this study was to determine whether a 9-week resistance training program based on high load (HL) versus low load combined with blood flow restriction (LL-BFR) induced a similar (i) distribution of muscle hypertrophy among hamstring heads (semimembranosus, SM; semitendinosus, ST; and biceps femoris long head, BF) and (ii) magnitude of tendon hypertrophy of ST, using a parallel randomized controlled trial.

METHODS

A total of 45 participants were randomly allocated to one of three groups: HL, LL-BFR, and control (CON). Both HL and LL-BFR performed a 9-week resistance training program composed of seated leg curl and stiff-leg deadlift exercises. Freehand 3D ultrasound was used to assess the changes in muscle and tendon volume.

RESULTS

The increase in ST volume was greater in HL (26.5 ± 25.5%) compared to CON (p = 0.004). No difference was found between CON and LL-BFR for the ST muscle volume (p = 0.627). The change in SM muscle volume was greater for LL-BFR (21.6 ± 27.8%) compared to CON (p = 0.025). No difference was found between HL and CON for the SM muscle volume (p = 0.178).There was no change in BF muscle volume in LL-BFR (14.0 ± 16.5%; p = 0.436) compared to CON group. No difference was found between HL and CON for the BF muscle volume (p = 1.0). Regarding ST tendon volume, we did not report an effect of training regimens (p = 0.411).

CONCLUSION

These results provide evidence that the HL program induced a selective hypertrophy of the ST while LL-BFR induced hypertrophy of SM. The magnitude of the selective hypertrophy observed within each group varied greatly between individuals. This finding suggests that it is very difficult to early determine the location of the hypertrophy among a muscle group.

Six Weeks of Unilateral Flywheel Hip-Extension and Leg-Curl Training Improves Flywheel Eccentric Peak Power but Does Not Enhance Hamstring Isokinetic or Isometric Strength

PURPOSE

This preregistered trial investigated how 6 weeks of unilateral flywheel leg-curl and hip-extension training impact isokinetic, isometric, and flywheel strength and power outcomes.

METHODS

The study involved 11 male university athletes (age 22 [2] y; body mass 77.2 [11.3] kg; height 1.74 [0.09] m) with one leg randomly allocated to flywheel training and one leg to control. Unilateral eccentric and isometric knee-flexion torque and flywheel unilateral leg-curl and hip-extension peak power were tested. Training intensity and volume (3-4 sets of 6 + 2 repetitions) were progressively increased.

RESULTS

The intervention enhanced hip-extension concentric (P < .01, d = 1.76, large) and eccentric (P < .01, d = 1.33, large) peak power more than the control (significant interaction effect). Similarly, eccentric (P = .023, d = 1.05, moderate) peak power was enhanced for the leg curl. No statistically significant differences between conditions were found for isokinetic eccentric (P = .086, d = 0.77, moderate) and isometric (P = .431, d = 0.36, small) knee-flexor strength or leg-curl concentric peak power (P = .339, d = 0.52, small). Statistical parametric mapping analysis of torque-angle curves also revealed no significant (P > .05) time-limb interaction effect at any joint angle.

CONCLUSION

Unilateral flywheel hamstring training improved knee-flexor eccentric peak power during unilateral flywheel exercise but not flywheel concentric, isokinetic eccentric, or isometric (long-lever) knee-flexor strength.

The effects of hip- vs. knee-dominant hamstring exercise on biceps femoris morphology, strength, and sprint performance: a randomized intervention trial protocol

BACKGROUND

The hamstrings are an important muscle group that contribute to horizontal force during sprint acceleration and are also the most injured muscle group in running-based sports. Given the significant time loss associated with hamstrings injury and impaired sprinting performance following return to sport, identifying exercises that drive adaptations that are both protective of strain injury and beneficial to sprint performance is important for the strength and conditioning professional. This paper describes the study protocol investigating the effects of a 6-week training program using either the hip-dominant Romanian deadlift (RDL) or the knee-dominant Nordic hamstring exercise (NHE) on hamstring strain injury risk factors and sprint performance.

METHODS

A permuted block randomized (1:1 allocation) intervention trial will be conducted involving young, physically-active men and women. A target sample size of 32 will be recruited and enrolled participants will undergo baseline testing involving extended-field-of-view ultrasound imaging and shear wave elastography of the biceps femoris long head muscle, maximal hamstrings strength testing in both the RDL and NHE, and on-field sprint performance and biomechanics. Participants will complete the 6-week training intervention using either the RDL or NHE, according to group allocation. Baseline testing will be repeated at the end of the 6-week intervention followed by 2 weeks of detraining and a final testing session. The primary outcome will be regional changes in fascicle length with secondary outcomes including pennation angle, muscle cross sectional area, hamstring strength, and maximal sprint performance and biomechanics. An exploratory aim will determine changes in shear wave velocity.

DISCUSSION

Despite extensive research showing the benefits of the NHE on reducing hamstring strain injury risk, alternative exercises, such as the RDL, may offer similar or potentially even greater benefits. The findings of this study will aim to inform future researchers and practitioners investigating alternatives to the NHE, such as the RDL, in terms of their effectiveness in reducing rates of hamstring strain injury in larger scale prospective intervention studies.

TRIAL REGISTRATION

The trial is prospectively registered on ClinicalTrials.gov (NCT05455346; July 15, 2022).