Muscle size of individual hip extensors in sprint runners: Its relation to spatiotemporal variables and sprint velocity during maximal velocity sprinting

Relationship between individual hip extensor muscle size and sprint running performance: sprint phase dependence

The muscle size of the hip extensors has been suggested to be important in sprint running performance; however, reported findings are partly inconsistent. Here, we hypothesised that the association between hip extensor size and sprint performance may vary by sprint phase (early-acceleration, maximal-velocity and deceleration phases). To test this hypothesis, we measured the volumes of individual hip extensors of 26 male sprinters via magnetic resonance imaging and their sprint velocities for each 10-m interval during a maximal-effort 100-m sprint. Based on the sprint velocities, the maximal-velocity phase was determined for each sprinter. At the individual muscle level, the semimembranosus volume relative to body mass was positively correlated with sprint velocity only in the early-acceleration phase (0-10 m, r = 0.592, corrected p = 0.003). On the other hand, the semitendinosus volume relative to body mass was positively correlated with sprint velocities in the maximal-velocity (r = 0.483, corrected p = 0.020) and deceleration (90-100 m, r = 0.605, corrected p = 0.003) phases. These results show that the association between hip extensor size and sprint performance is not constant but changes through the sprint phases.

Optimizing Resistance Training for Sprint and Endurance Athletes: Balancing Positive and Negative Adaptations

Resistance training (RT) triggers diverse morphological and physiological adaptations that are broadly considered beneficial for performance enhancement as well as injury risk reduction. Some athletes and coaches therefore engage in, or prescribe, substantial amounts of RT under the assumption that continued increments in maximal strength capacity and/or muscle mass will lead to improved sports performance. In contrast, others employ minimal or no RT under the assumption that RT may impair endurance or sprint performances. However, the morphological and physiological adaptations by which RT might impair physical performance, the likelihood of these being evoked, and the training program specifications that might promote such impairments, remain largely undefined. Here, we discuss how selected adaptations to RT may enhance or impair speed and endurance performances while also addressing the RT program variables under which these adaptations are likely to occur. Specifically, we argue that while some myofibrillar (muscle) hypertrophy can be beneficial for increasing maximum strength, substantial hypertrophy can lead to macro- and microscopic adaptations such as increases in body (or limb) mass and internal moment arms that might, under some conditions, impair both sprint and endurance performances. Further, we discuss how changes in muscle architecture, fiber typology, microscopic muscle structure, and intra- and intermuscular coordination with RT may maximize speed at the expense of endurance, or maximize strength at the expense of speed. The beneficial effect of RT for sprint and endurance sports can be further improved by considering the adaptive trade-offs and practical implications discussed in this review.

Acute impact of Nordic hamstring exercise on sprint performance after 24, 48 and 72 hours

The Nordic Hamstring Exercise (NHE) improves the strength of the hamstring muscles, as well as prevents and rehabilitates the injuries of said muscles. However, the eccentric demand of NHE may influence the athlete's performance, making compliance with these programmes difficult. The aim is to analyse the acute impact on sprint performance after the passing of 24, 48, and 72 hours respectively since an NHE-based session (4 sets of 10 repetitions) had taken place. Participants were randomly divided into an experimental group (EG) (n = 12 male participants) who carried out an NHE session and a measurement of their 30 m sprint performance in each of the three subsequent days, and a control group (CG) (n = 12 male participants) who did not take part in the NHE session. The results show a significant reduction of maximum power within 24 hours (t = 3.57, d = 0.22, P < .0273) as well of the production of high speed horizontal force up to after 48 hours (t = 4.82, d = 0.22, P < .0001) in the EG. These results may suggest separating weekly NHE sessions from competition or demanding training in which sprint performance should not be affected by at least 72 hours.

Muscle morphological changes and enhanced sprint running performance: A 1-year observational study of well-trained sprinters

Numerous cross-sectional studies have attempted to identify the muscle morphology required to achieve high sprint velocity. Our longitudinal study addressed an unanswered question of cross-sectional studies: whether hypertrophy of the individual trunk and thigh muscles induced by daily training (e.g., sprint, jump, and resistance training) is linked to an improvement in sprint performance within well-trained sprinters. Twenty-three collegiate male sprinters (100-m best time of 11.36 ± 0.44 s) completed their daily training for 1 year without our intervention. Before and after the observation period, the sprint velocities at 0-100 m, 0-10 m, and 50-60 m intervals were measured using timing gates. The volumes of 14 trunk and thigh muscles were measured using magnetic resonance imaging. Muscle volumes were normalized to the participants' body mass at each time point. Sprint velocities increased at the 0-100 m (p < 0.001), 0-10 m (p = 0.019), and 50-60 m (p = 0.018) intervals after the observation period. The relative volumes of the tensor fasciae latae, sartorius, biceps femoris long head, biceps femoris short head, semitendinosus, and iliacus were increased (all p < 0.050). Among the hypertrophied muscles, only the change in the relative volume of the semitendinosus was positively correlated with the change in sprint velocity at the 50-60 m interval (p = 0.018 and ρ = 0.591). These findings suggest that semitendinosus hypertrophy seems to be associated with sprint performance improvement within well-trained sprinters during the maximal velocity phase.

Muscle Morphology Does Not Solely Determine Knee Flexion Weakness After Anterior Cruciate Ligament Reconstruction with a Semitendinosus Tendon Graft: A Combined Experimental and Computational Modeling Study

The distal semitendinosus tendon is commonly harvested for anterior cruciate ligament reconstruction, inducing substantial morbidity at the knee. The aim of this study was to probe how morphological changes of the semitendinosus muscle after harvest of its distal tendon for anterior cruciate ligament reconstruction affects knee flexion strength and whether the knee flexor synergists can compensate for the knee flexion weakness. Ten participants 8-18 months after anterior cruciate ligament reconstruction with an ipsilateral distal semitendinosus tendon autograft performed isometric knee flexion strength testing (15°, 45°, 60°, and 90°; 0° = knee extension) positioned prone on an isokinetic dynamometer. Morphological parameters extracted from magnetic resonance images were used to inform a musculoskeletal model. Knee flexion moments estimated by the model were then compared with those measured experimentally at each knee angle position. A statistically significant between-leg difference in experimentally-measured maximal isometric strength was found at 60° and 90°, but not 15° or 45°, of knee flexion. The musculoskeletal model matched the between-leg differences observed in experimental knee flexion moments at 15° and 45° but did not well estimate between-leg differences with a more flexed knee, particularly at 90°. Further, the knee flexor synergists could not physiologically compensate for weakness in deep knee flexion. These results suggest additional factors other than knee flexor muscle morphology play a role in knee flexion weakness following anterior cruciate ligament reconstruction with a distal semitendinosus tendon graft and thus more work at neural and microscopic levels is required for informing treatment and rehabilitation in this demographic.

The Lower Limbs of Sprinters Have Larger Relative Mass But Not Larger Normalized Moment of Inertia than Controls

PURPOSE

Sprinters exhibit inhomogeneous muscularity corresponding to musculoskeletal demand for sprinting execution. An inhomogeneous morphology would affect the mass distribution, which in turn may affect the mechanical difficulty in moving from an inertia perspective; however, the morphological characteristics of sprinters from the inertia perspective have not been examined. Here we show no corresponding differences in the normalized mass and normalized moment of inertia between the sprinters and untrained nonsprinters.

METHODS

We analyzed fat- and water-separated magnetic resonance images from the lower limbs of 11 male sprinters (100 m best time of 10.44-10.83 s) and 12 untrained nonsprinters. We calculated the inertial properties by identifying the tissue of each voxel and combining the literature values for each tissue density.

RESULTS

The lower-limb relative mass was significantly larger in sprinters (18.7% ± 0.7% body mass) than in nonsprinters (17.6% ± 0.6% body mass), whereas the normalized moment of inertia of the lower limb around the hip in the anatomical position was not significantly different (0.044 ± 0.002 vs 0.042 ± 0.002 [a. u.]). The thigh relative mass in sprinters (12.9% ± 0.4% body mass) was significantly larger than that in nonsprinters (11.9% ± 0.4% body mass), whereas the shank and foot relative masses were not significantly different.

CONCLUSIONS

We revealed that the mechanical difficulty in swinging the lower limb is not relatively larger in sprinters in terms of inertia, even though the lower-limb mass is larger, reflecting their muscularity. We provide practical implications that sprinters can train without paying close attention to the increase in lower-limb mass and moment of inertia.

Semitendinosus muscle morphology in relation to surface electrode placement in anterior cruciate ligament reconstructed and contralateral legs

The semitendinosus tendon is commonly harvested as graft tissue for anterior cruciate ligament reconstruction (ACLR). Although the semitendinosus tendon can regenerate following harvesting, ACLR results in substantial reductions in semitendinosus muscle size and length, potentially complicating electrode placement for electromyography. The purpose of this study was to assess whether the most commonly used electrode placement [recommended by the "Surface Electromyography for Non-Invasive Assessment of Muscles" (SENIAM) project] is appropriate for measuring semitendinosus electromyograms after ACLR. In nine participants (unilateral ACLR with a semitendinosus graft), B-mode ultrasonography was used to bilaterally determine (i) the semitendinosus muscle-tendon junction position and the state of tendon regeneration (latter for the ACLR leg only) and (ii) the anatomical cross-sectional area (ACSA) of the semitendinosus muscle at the SENIAM-recommended electrode placement site at rest and during isometric maximal voluntary contraction (MVC) at two knee joint angles. Depending on the contraction state and joint angle, the semitendinosus muscle had retracted past the recommended placement site in 33-78% of ACLR legs, but not in any contralateral legs. The ACSA of semitendinosus was smaller both at rest and MVC in the ACLR compared to contralateral leg. The ACSA for both legs decreased at MVC compared to rest and at deep compared to shallow knee flexion angles, likely due to sliding of the muscle under the skin. These results suggest SENIAM guidelines are likely unsuitable for recording surface electromyograms from the semitendinosus muscle after tendon harvesting for ACLR as the muscle of interest may not be within the electrode detection volume.

Measuring Muscle Activity in Sprinters Using T2-Weighted Magnetic Resonance Imaging

PURPOSE

This study aimed to investigate the level of muscle activity during sprint running using T2-weighted magnetic resonance imaging.

METHODS

Fourteen male sprinters (age 21.2 [4.0] y; height 171.8 [4.2] cm, weight 65.5 [5.3] kg, 100-m personal record 11.01 [0.41] s; mean [SD]) performed 3 sets of three 60-m round-trip sprints. Before and after the round-trip sprints, 3 T magnetic resonance imaging scans were performed to obtain the T2 values of the 14 athletes' lower-extremity muscles.

RESULTS

After the 60-m round-trip sprints, the T2 value of the gluteus maximus, long head of biceps femoris, semitendinosus, semimembranosus, adductor brevis, adductor longus, adductor magnus, and gracilis increased significantly. The rate of change in the T2 values before and after the 60-m round-trip sprints was notably higher in the semitendinosus and gluteus maximus than in the other muscles.

CONCLUSIONS

These findings demonstrate the specific physiological metabolism of the lower-extremity muscles during fast sprinting. There are particularly high levels of muscle activity in the gluteus maximus and semitendinosus during sprint performance.