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How muscles maximize performance in accelerated sprinting.

The best sprinters run at an average speed of approximately 10 m/s and can reach maximum speeds of nearly 13 m/s during a 100 m race. Previous studies have analyzed function of the individual lower-limb muscles at various steady-state running speeds, including sprinting. Similar analyses have not been undertaken for the acceleration phase of maximum-effort sprinting beyond the first two steps. As a result, there are no data that describe how individual muscles work synergistically to increase the forward momentum of the body beyond the first two foot contacts of accelerated sprinting. This is an important knowledge gap as top sprinters in a 100 m race attain their maximum speeds after a 30 to 50 m acceleration phase.

Fundamental knowledge of muscle function during maximum acceleration sprinting is important for the design of athletic training regimens aimed at optimizing sprinting performance and for the development of more effective injury prevention and rehabilitation practices.

The aim of this study was to provide a better understanding of how the lower-limb muscles maximize performance during accelerated sprinting. The primary aim was to describe and explain the contributions of individual muscles to the vertical and fore-aft GRF impulses generated for the majority of the acceleration phase (19 foot contacts) of a maximal sprint. The authors were interested specifically in identifying those muscles responsible for increasing the forward momentum of the body at each step.

Five sub-elite sprinters (4 males, 1 female; age, 21.8 ± 3.2 years; height, 180.0 ± 8.3 cm; body mass, 73.6 ± 7.6 kg) with no pre-existing musculoskeletal injuries participated in the study. All participants regularly competed in sprint events between 100-400 m, with personal best times for 100 m ranging from 10.4 seconds to 12.7 seconds.

Gait experiments were performed on a straight 110 m indoor track. Each participant was required to accelerate as quickly as possible from a static three-point crouched position until the end of the capture volume before decelerating to rest. Full-body motion, GRF, and muscle EMG data were recorded for the first 19 foot contacts of the acceleration phase in stages by adjusting the location of the starting position with respect to the first force plate.

A 3D motion analysis system with 22 VICON cameras each sampling at 250 Hz was used to measure full-body motion while GRFs were recorded from 8 force plates each measuring 900 × 600 mm2 in size and sampling at 1500 Hz. Muscle EMG data were recorded from five muscles: medial hamstrings (i.e., combined signals from semimembranosus and semitendinosus), vastus medialis and lateralis, lateral gastrocnemius, and soleus.

Computer simulations of the acceleration phase of sprinting were generated based on a generic model of the body. Participant-specific musculoskeletal models were created by scaling the generic model to eachparticipant’s height and body mass. Participant-specific computer simulations of the first 19 foot contacts of the acceleration phase were then generated; altogether, 95 participant-specific simulations were generated for all 19 foot contacts across the 5 participants.

Each muscle’s contribution to the GRF impulse was summed over all 19 foot contacts to determine its total contribution over the acceleration phase. This summation was done for the fore-aft and vertical GRF impulses separately. Using these data, the authors classified each muscle as a ‘supporter’ and/or ‘accelerator/brake’. A muscle was classified as a ‘supporter’ if its total contribution to the vertical GRF impulse was positive (i.e., overall it delivered an upward impulse to the body). A muscle was classified as an ‘accelerator’ if its total contribution to the fore-aft GRF impulse was positive (i.e., overall it generated a propulsive impulse that increased forward momentum of the body), and it was classified as a ‘brake’ if its contribution to the fore-aft GRF impulse was negative (i.e., overall it generated a backward impulse that retarded forward momentum of the body).

The ankle plantarflexors played a major role in generating the support and increase in forward momentum needed to progress sprinting speed toward upper limits. Soleus acted primarily as a supporter and provided a substantial fraction of the upward impulse (44%) at each foot contact. Gastrocnemius generated most of the propulsive impulse (37%) but also contributed to the upward impulse and therefore functioned as both an accelerator and supporter. The hamstrings and gluteus medius developed extensor moments about the hip and functioned primarily as accelerators by contributing appreciably to the increase in forward momentum of the body; however, the hamstrings also accelerated the body downward and detracted from support. The vasti and rectus femoris functioned primarily as supporters, but these muscles also retarded forward momentum at each foot contact and acted as brakes. Gluteus maximus contributed relatively little to either the propulsive or support impulse. Overall, the ankle plantarflexors and hip extensors/abductors functioned as accelerators whereas the knee extensors acted as a brake. The ankle plantarflexors and knee extensors generated nearly all of the support impulse at each foot contact.

The findings of this study will be of interest to coaches striving to optimize sprint performance in elite athletes, as well as sports medicine clinicians aiming to improve injury prevention and rehabilitation practices.

Source:

Pandy MG et al. (2021) How muscles maximize performance in accelerated sprinting. Scandinavian Journal of Medicine & Science in Sports.

Link to the Paper:

Here

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