Muscle metabolism, lactate breaking point, and biomechanical features of endurance running.

Nine subjects ranging in muscle fiber composition (m, vastus lateralis) from 38% to 100% slow twitch (ST) were filmed while running on a treadmill at a speed corresponding to the onset of blood lactate accumulation (VOBLA). The film analysis concentrated on several kinetic features of running, such as mechanical work (W) and average power output (W) for the total step cycle including the positive and negative work phases. The results indicated that %ST was related significantly (r = 0.78) with VOBLA and with the average speed of a marathon race (Vm; r = 0.80), which followed the treadmill test. The values of VOBLA and Vm were 4.27 +/- 0.51 and 3.74 +/- 0.64 m x s-1, respectively. Capillary density as calculated from amylase PAS staining of the muscle samples demonstrated also a significant relationship with Vm (r = 0.80). The value of W was not significantly related to either %ST or VOBLA. However, the average mechanical power output at VOBLA (WOBLA) demonstrated high correlations with %ST (r = 0.75), VOBLA (r = 0.90), Vm (r = 0.92), and with capillary density (r = 0.77). The findings suggest that mechanical power at VOBLA is an important parameter, which indicates the maximum power output of the runner under pure aerobic conditions.