A treadmill protocol to investigate independently the metabolic and mechanical stress of exercise

The purpose of this study was to describe an experimental treadmill model for the independent assessment of metabolic and mechanical stress associated with exercise. Eight well-trained male runners (VO₂ max 61.2 ml.kg^-1.min^-1) undertook, on different days, three 40 min bouts (consisting of 8 x 5 min work intervals) of treadmill running: uphill, downhill and near-level. Mean %VO₂ max was 90.0, 52.7 and 52.2 for uphill, near-level and downhill running respectively. Oxygen uptake increased (p<0.05) across the eight work intervals during uphill running, with non-significant increases in both near-level and downhill running. In contrast, heart rate increased (p<0.05) which uphill and downhill, but not near-level running. Blood lactate concentration was higher (p<0.01) and plasma pH lower (p<0.01) after uphill running compared with downhill and near-level running. Plasma creatine kinase activity was elevated (p<0.05) immediately after uphill running and 24 hours after downhill running (p<0.05). Subjective rating of delayed onset muscle soreness was elevated (p<0.05) at 24 and 48 hours after downhill running only. There were no significant changes in the plasma concentration of the inflammatory mediators interleukin-1β, complement component C3a and C-reactive protein. Given the observed differences in cardiorespiratory responses and indicators of muscle damage and soreness, this experimental model could be employed to investigate, independently, the metabolic and mechanical stress of exercise.