In order to best train to improve maximum sprinting, a good understanding of the requirements of the muscles involved in this motion must be understood. The muscles must perform two tasks during sprinting: first, they must produce force to propel the body horizontals; second, they must produce a vertical force to counteract the pull of gravity. These forces must be produced during the support phase of sprinting.
During the beginning of the stance phase, the quadriceps eccentrically contract (contract while being lengthened) to stabilize the knee. They then concentrically contract at the end of the support phase to propel the body upward for the flight phase. During the support phase of sprinting, the glute medius contracts along with the oblique muscles of the abdomen to stabilize the pelvis (Wiemann and Tidow).
The muscle with the longest duration of activity during sprinting is the hamstrings. They begin firing during the back-swing and ends at the start of forward-swing phase. This suggests the importance of the hamstrings in providing hip extension forces to propel the body forward. Also that the knee flexion following the foot leaving the ground is not due solely to inertia but by active contraction of the hamstrings (Wiemann and Tidow).
The vastus medius (VM) activity is much shorter than the hamstrings. Approximately 30ms before the foot makes contact with the ground, the VM becomes active. After contact, the muscle activity continues for only 30-50ms. This supports the idea that the quadriceps are more important in their role in eccentrically controlling knee flexion and produce little of the force for forward propulsion of the body. However, during the sprint start, VM plays a much lager role in forward propulsion of the body due to the forward angle of the body during the sprint start (Wiemann and Tidow).
Glute max (GM) activity begins during the back-swing phase with the hamstrings to produce downward acceleration of the leg. GM activity ceases in mid support phase around the same time as the VM (Wiemann and Tidow). The GM “contributes to vertical support after initial foot contact through delivery of power to the trunk, as a contributor to horizontal propulsionor braking and for deceleration of the limb at the end of swing (Bartlett).
30ms before the leg reaches the ground the adductor magnus activity stops. This is because once the leg is supporting bodyweight, gravity provides an adduction moment. Thus the glute max must continue to work during the support phase to stabilize the pelvis and prevent the pelvis of the swing from dropping. The adductor magnus (AM) is unique in that it works as a hip extender and hip flexor at different points of the gait cycle depending on the location of the thigh in relation to the AM’s origin (Wiemann and Tidow).
When looking at EMG data during sprinting, a few interesting things can be found regarding muscle activation levels. First, the levels of muscle recruitment of all tested muscles while running are higher than those seen during a maximum voluntary isometric contraction (MVIC). This suggests supraspinal regulation allows for motor units to fire faster while sprinting than during an MVIC and/or that motor units go un-recruited during an MVIC but are activated with sprinting. Also interesting is that the highest degree of muscle activity is seen during the back-swing phase rather than the support phase. Research has shown that sprinting performance is dependent of the velocity during back-swing (Wiemann and Tidow).
The role of the arm swing is another important consideration in sprint technique. In a 100m sprint, sprinting without an arm spring has been shown to decrease speed by ~10% (Wiemann and Tidow).
In conclusion, during the starting section of a sprint, the VM plays a large role in forward propulsion of the body. But, after the starting section of a full-speed sprint the hip extensors are more important for horizontal velocity (Wiemann and Tidow).
- Wiemann and Tidow (1995). Relative Activity of Hip and Knee Extensors in Sprinting – Implications for Training. New Studies in Athletics, 10, 29-49.
- Bartlett, Sumner, Ellis, and Kram (2014). Activity and Functions of the Human Gluteal Muscles in Walking, Running, Sprinting, and Climbing. American Journal of Physical Antropology, 153, 124-131.