Neuromuscular Responses Of Running To Exhaustion At The Velocity Associated With Maximal Oxygen Uptake

The concept “vVO2max” is defined as the minimum running velocity that elicits maximal oxygen uptake (VO2max). PURPOSE: To examine the neuromuscular responses of the thigh and leg during a run to exhaustion at vVO2max in elite runners. METHODS: Fifteen subjects (males: n = 10, females, n = 5; mean age ± SD = 21.7 ± 1.7 years; body mass = 68.8 ± 9.9 kg; running volume = 65.0 ± 41.8 km·wk-1) volunteered to visit the laboratory on two occasions. The first laboratory visit involved an incremental treadmill test to exhaustion with the measurement of gas exchange using a calibrated metabolic cart that began at 9.0 km·h-1 (females) or 10.0 km·h-1 (males) and increased 1.0 km·h-1 every two minutes until volitional fatigue for determination of their VO2max and vVO2max. For the second laboratory visit, wireless electromyographic (EMG) electrodes were placed on the right thigh and leg over the vastus lateralis, semitendinosus, and medial gastrocnemius muscles. Following a warm-up, each subject ran on the treadmill at a constant velocity of their vVO2max to volitional exhaustion. A two-way analysis of variance (ANOVA) with repeated measures was used to determine significant (p < 0.05) mean differences in normalized EMG amplitude (%) for the three muscles across normalized time to exhaustion (%TTE). Follow-up analyses included one-way ANOVAs with repeated measures and paired-samples t-tests. RESULTS: The mean values for VO2max, vVO2max, and TTE at vVO2max were 63.2 ± 9.3 mL·kg-1 min-1, 16.0 ± 2.0 km·h-1, and 5.38 ± 1.03 minutes, respectively. For normalized EMG amplitude, there was no significant muscle x TTE interaction (F(8,112) = 1.605; p = 0.131; partial ɳ2 = 0.103) or main effect for muscle (F(2,28) = 0.298; p = 0.745; partial ɳ2 = 0.021), but there was a significant main effect for time (F(4,56) = 41.223; p < 0.001; partial ɳ2 = 0.747). Follow-ups indicated that estimated marginal means (collapsed across muscle) for normalized EMG amplitude decreased with each subsequent time point during the run to exhaustion (20%TTE = 89.2 ± 5.4% > 40%TTE = 82.4 ± 4.3% > 60%TTE = 78.8 ± 6.3% > 80%TTE = 77.1 ± 6.7% > 100%TTE = 73.4 ± 6.4%). CONCLUSIONS: These findings indicated that fatigue-induced decreases in muscle activation (as reflected by EMG amplitude) remain consistent across muscles of the thigh and leg while maintaining vVO2max in college-aged runners.