Neuromuscular Responses Of The Quadriceps Femoris And Hamstring Muscles During Incremental Treadmill Running

Abstract

PURPOSE: The purpose of the present study was to examine the patterns of responses for the electromyographic (EMG) amplitude versus oxygen uptake (VO2) relationships from muscles of the quadriceps femoris and hamstrings during incremental treadmill running. METHODS: Thirteen aerobically-trained males (mean age ± SD = 21.4 ± 1.4 yrs, body mass = 73.8 ± 7.0 kg, 6.8 ± 2.5 aerobic training hr·wk-1, 58.4 ± 49.6 running km·wk-1) volunteered to perform an incremental treadmill test to exhaustion that began at 9.7 km·h-1 and increased 1.6 km·h-1 every two minutes. Following the 14.5 km·h-1 stage, the grade was increased 2.5% every two minutes until volitional fatigue. Expired gas samples were collected and analyzed using a calibrated metabolic cart with VO2 values expressed as 30-second averages and normalized to peak oxygen uptake (VO2peak). Electromyographic samples were recorded using bipolar wireless electrode sensors that were placed on the right thigh over the vastus lateralis, rectus femoris, vastus medialis, biceps femoris, and semitendinosus muscles. Electromyographic amplitude (μVrms) values were calculated for 30-second epochs, normalized, and separately plotted across VO2 for each muscle and subject. Polynomial regression analyses were used to determine the best model fit (i.e. linear, quadratic, or cubic) for the EMG amplitude versus VO2 relationships for the composite data. RESULTS: The results of the polynomial regression analyses indicated there were significant (P < 0.05) increases in EMG amplitude across VO2 for the vastus lateralis (linear, r = 0.970), rectus femoris (cubic, r = 0.976), vastus medialis (quadratic, r = 0.997), biceps femoris (cubic, r = 0.999), and semitendinosus muscles (linear, r = 0.992). CONCLUSIONS: The findings of the present study indicated that the patterns of responses (i.e. linear, quadratic, cubic) for muscle activation (EMG amplitude) versus exercise intensity (VO2) appear to be unique among muscles of the thigh and may be due to variations in muscle architecture, fiber type, or biomechanical differences. In addition, these patterns of responses for muscle activation relative to exercise intensity may provide foundational data related to the assessment of neuromuscular fatigue in the quadriceps femoris and hamstring muscles during incremental treadmill running.