Q.The physiological factor that contributes MOST to an athlete's maximum sprinting speed is:

Maximum sprinting speed depends on the ability to generate explosive force in a very short time. Muscle fibres are classified by their contractile properties: Type I fibres contract slowly and are fatigue-resistant, making them ideal for endurance activities like marathon running. Type II fibres contract rapidly and powerfully but fatigue quickly, which is exactly what sprinting demands. Elite sprinters typically have 70–80% Type II fibres in their leg muscles, allowing them to produce the high force and velocity needed for acceleration and top speed over distances like 100 m or 200 m.

(a) is wrong because Type I (slow-twitch) fibres are optimized for sustained, low-intensity effort — they generate less force per contraction and cannot support the explosive power required in sprinting. …

Why muscle fibre type governs sprint performance

Sprinting is an explosive, high-intensity activity lasting only a few seconds. The neuromuscular system must generate maximum force in minimal time, and the type of muscle fibre recruited determines how quickly and powerfully a muscle can contract.

Human skeletal muscle contains two principal fibre types. Type I fibres (slow-twitch) are fatigue-resistant and rely on aerobic metabolism; they sustain prolonged, low-intensity efforts like distance running. Type II fibres (fast-twitch) contract two to three times faster, produce greater peak force, and depend on anaerobic pathways—glycolysis and the phosphagen system—that deliver energy almost instantaneously. Elite sprinters typically possess 70–80 % Type II fibres in their leg muscles, a distribution largely determined by genetics and reinforced by sprint training.

During a 100 m dash the athlete accelerates for roughly 6 seconds and holds top speed for another 3–4 seconds. Peak velocity is reached when the ground-contact time per stride becomes so short—often under 0.09 seconds—that only the fastest-contracting fibres can complete a force cycle. Type II fibres excel in this regime because their myosin ATPase hydrolyzes ATP rapidly, their sarcoplasmic reticulum releases and re-sequesters calcium quickly, and their cross-bridge cycling rate is high. The result is a stride frequency that can exceed 5 Hz and a ground-reaction force several times body weight.

Now consider the other options. A high bone mineral density (option c) supports skeletal integrity under impact but adds no contractile speed; in fact, unnecessarily heavy bones would raise inertia and slow limb swing. A large body weight (option d) increases the absolute force required to accelerate the center of mass, which is why sprinters are lean and muscular rather than heavy. Type I fibres (option a) are precisely the wrong tool: their slow contraction velocity and reliance on oxygen make them suited to marathons, not the 10-second all-out effort of a sprint.

Evaluation of each option …