Neuromuscular Activation Patterns of the Gastrocnemius Muscle During Static and Dynamic Sprint Starts: Implications for Acceleration Training

Objective: The gastrocnemius muscle is crucial in explosive acceleration, yet the effect of sprint start type [static (began from an upright stance) vs. dynamic (included bilateral hops before sprinting)] on its activation remains underexplored. Methods: This study compared medial and lateral gastrocnemius activation during the first four contacts of 4 m sprints in 34 physically active males (24.13 ± 3.43 years) using surface electromyography normalized to peak sprint values. A two-way repeated-measures ANOVA (condition × foot contact) was used as the primary omnibus test (α < 0.05); given the significant interaction, simple-effects analyses—repeated-measures ANOVA within each start type and paired t-tests at each foot contact—were subsequently conducted, with the four pointwise start-type comparisons corrected for multiplicity using the Holm–Bonferroni method. Results: Overall gastrocnemius activation did not differ between conditions (static: 72.5% vs. dynamic: 71.7% of peak sprint EMG (p = 0.488, d = 0.12), and a significant condition × foot contact interaction (p = 0.001) confirmed that the temporal profile of activation across foot contacts differed between start types. Decomposing this interaction, the second foot contact showed the highest activation during static starts (significantly exceeding first and fourth, though not third foot contact), whereas during dynamic starts, the first contact was significantly lower than the second, third and fourth—which did not differ from one another. Between-condition comparisons at each foot contact showed that static starts exhibited a non-significant trend toward higher activation at the first and second foot contacts (p = 0.055 and p = 0.056, not significant after Holm–Bonferroni), while dynamic starts showed significantly greater activation at the fourth foot contact (p = 0.005, d = 0.52), the only pointwise comparison that survived correction for multiple comparisons (p_Holm = 0.02). Conclusions: These findings indicate an overall difference in the temporal pattern of GA activation between start types, with DS showing greater activation than SS at FC4, the only pointwise between-condition difference that survived multiplicity correction. Because activation did not differ among FC2, FC3, and FC4 within DS, the data do not demonstrate that the activation peak shifted specifically to FC4; furthermore, this EMG pattern does not demonstrate a reduction in muscle force, tendon strain, whole-limb mechanical loading, or injury risk, whereas the apparently higher early-phase activation in static starts at the first- and second-foot contacts should be interpreted as a non-significant trend, pending confirmation in larger samples. Sprint start type modulates gastrocnemius activation; whether these activation patterns translate into differences in performance or mechanical loading should be tested using concurrent kinetic, kinematic, and multi-muscle measurements.