Nueromuscular Responses During Dynamic Resistance Exercise In The Extreme And Severe Intensity Domains

Intensity domains (moderate, heavy, severe, extreme) are demarcated by distinct physiological responses for whole-body dynamic exercise, but are not clearly defined for dynamic constant external resistance exercise. Neuromuscular efficiency (NME) and electromyographic amplitude (AMP) may provide insight on physiological responses during fatiguing resistance exercise across intensity domains. PURPOSE: To examine the neuromuscular responses during severe (SEV; >2 min) and extreme (EXT; <2 min) resistance exercise. METHODS: Ten participants (22 ± 1 yrs) performed a 1 repetition maximum (1RM) and repetitions to failure at 10% 1RM (SEV; 85 ± 38 reps) and 70% 1RM (EXT; 9 ± 4 reps) for single-limb leg extension on separate days. AMP was measured from the vastus lateralis and normalized as a percent of 1RM (%1RM). NME was calculated as the ratio between load (kg) to AMP (%1RM). Comparisons across time (First, Middle, and Last 10% of repetitions completed) were made using one-way repeated measures ANOVAs for SEV and EXT intensities. RESULTS: For SEV, AMP increased (First: 31.9 ± 19.7% < Middle: 53.9 ± 31.0% < Last: 92.1 ± 63.6%; p ≤ 0.035) and NME decreased (First: 0.665 ± 0.37 kg/% > Middle: 0.375 ± 0.19 kg/% > Last 0.230 ± 0.15 kg/%; p ≤ 0.011) across each timepoint. For EXT, AMP increased from the First (95.6 ± 57.6%) to Last 10% (128.4 ± 60.5%, p < 0.001) but not from the First to Middle 10% (116.31 ± 49.3, p = 0.111) or from the Middle to Last 10% (p = 0.262). NME for EXT decreased from the First (1.46 ± 0.6 kg/%) to Middle 10% (1.14 ± 0.5 kg/%, p = 0.021), but did not change from the Middle to Last 10% (1.03 ± 0.4 kg/%, p = 0.064). CONCLUSIONS: For SEV, AMP increased and NME decreased during the initial stage of leg extension exercise and as task failure approached. For EXT, AMP did not change and NME was reduced during the initial stage of exercise. As leg extension exercise reached task failure, both AMP and NME did not change for EXT.