Exhaustive treadmill running decreased the mean Hmax/Mmax ratio from 0.61 to 0.31 in trained runners, indicating significant suppression of spinal excitability (p < 0.0001).
Does treadmill running to exhaustion alter spinal excitability (Hmax/Mmax ratio) in trained runners?
Treadmill running to exhaustion induces heterogeneous changes in spinal excitability among trained runners, highlighting different physiological profiles of neuromuscular fatigue.
Effect estimate: Partial eta squared for Time effect 0.88 (95% CI 95% CI [0.80, 0.90] for Time effect)
Absolute Event Rate: 0.31% vs 0.61%
p-value: p=<0.0001
Background/Objectives: Spinal excitability may undergo adaptive modulation in response to training load, sport-specific demands, and fatigue. While high-impact sports are known to influence reflex responsiveness, the extent to which these changes differ from athletes in lower-impact disciplines remains unclear. This study aimed to investigate post-exercise changes in Hmax/Mmax ratio among trained runners with varied sport backgrounds, and to identify emergent physiological profiles that may reflect differential spinal adaptation to fatigue. Methods: Twenty-two trained athletes underwent unilateral H-reflex testing before and after treadmill running performed to voluntary exhaustion. Amplitudes of the H-reflex and M-wave were recorded, and Hmax/Mmax ratios were analyzed. Based on a physiologically relevant threshold commonly used to distinguish normal from suppressed reflex amplitudes, participants were post hoc classified into three groups: Group A (pre- and post-test ratios above threshold), Group B (pre above, post below), and Group C (both below). A two-way repeated-measures ANOVA was used to assess between-group effects. Results: Significant differences were found across groups and conditions (p < 0.001). Group A maintained reflex ratios above the threshold, indicating stable excitability. Group B showed the greatest suppression (approximately 66%), transitioning from normal to subthreshold values. Group C remained consistently below-threshold. A significant interaction (p < 0.0001) confirmed that reflex modulation varied by physiological profile. A small but statistically significant reduction in H-reflex latency was also observed; however, this change remained within normal physiological variability. Conclusions: Postexercise H-reflex modulation revealed heterogeneous neuromuscular responses among athletes. These findings may contribute to understanding how sport-specific demands and fatigue shape spinal excitability and may help identify individuals with adaptive or potentially pathological profiles relevant to sports diagnostics.
Silva et al. (2026) studied Healthy trained runners aged 18-23 years without diagnosed musculoskeletal or neurological disorders (n=22). Exhaustive treadmill running vs. Pre-exercise baseline measurement was evaluated on Hmax/Mmax ratio before and 15 minutes after exhaustive treadmill running (Partial eta squared for Time effect 0.88, 95% CI 95% CI [0.80, 0.90] for Time effect, p=<0.0001). Exhaustive treadmill running decreased the mean Hmax/Mmax ratio from 0.61 to 0.31 in trained runners, indicating significant suppression of spinal excitability (p < 0.0001).
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