Influence of muscle fibre type and fitness on the oxygen uptake/power output slope during incremental exercise in humans

Abstract

We recently reported that a higher percentage of type I fibres in vastus lateralis and a greater peak oxygen uptake (O2) were associated with a greater initial rise in O2 (O2 /W, where W is work rate) following the onset of heavy constant power output exercise (above the lactate threshold, LT). It was unclear if these results were true only for heavy exercise, or if the association between fibre type and/or fitness and O2 /W would also be seen for moderate (< LT) exercise. The purpose of the present study was to compare the relationships between fibre type or peak O2 and O2 /W determined for moderate (< LT) and heavy (> LT) exercise intensities during incremental exercise. Nine healthy subjects performed an incremental ramp test on a cycle ergometer. The O2 /Wslope was calculated for the domain of power outputs up to the LT (S1), from the LT towards peak O2 (S2), and over the entire linear portion of the O2 /W response (ST), and compared to fibre type distribution determined from biopsy of the vastus lateralis, and to peak O2 (as ml kg-1 min-1). Significant correlations between O2 /W and the proportion of type I fibres were found for each exercise domain (r is 0.69, 0.71 and 0.84 for S1, S2 and ST, respectively, P < 0.05). S1 ranged between about 9 ml min-1 W-1 for a low proportion of type I fibres and 11 ml min-1 W-1 for a high proportion of type I fibres. Similar correlations were also found between S2 (r = 0.70) and ST (r = 0.76) and peak O2. These results are consistent with our previous findings during > LT constant power output exercise, and suggest that the proportion of type I fibres, and possibly fitness as indicated by peak O2, is associated with greater O2 /W during the initial adjustment to < LT as well as > LT exercise. These results do not appear to be explained by classical descriptions of the kinetics of adjustment of O2 following the onset of ramp or constant power output exercise. They might reflect enhanced motor unit recruitment in subjects with a greater percentage of type I fibres, and/or who are more aerobically fit. However, the underlying mechanism for these findings must await further study.

Slow component of V̇O2 kinetics: the effect of training status, fibre type, UCP3 mRNA and citrate synthase activity

“…Therefore it is possible that the two groups may not have been exercising at the same relative intensity and our results must be interpreted with this in mind. We attempted to set the relative intensity for both groups at 50% of the difference between the LT and V O 2peak power outputs as this intensity has been shown to produce a SC, 22,42 however there are always methodological concerns when trying to normalise exercise intensities between two different groups. However, our study has provided some novel findings both within and between the Tr and RA groups.…”

Relationship between work rate and oxygen uptake in mitochondrial myopathy during ramp-incremental exercise

“…In order to measure the kinetics of the initial O 2 adjustment during the incremental exercise, the mean response time (MRT) was determined as the time from the onset of the ramp forcing function to the point of intersection between the baseline O 2 and a linear backward extrapolation of the O 2 vs time slope (Figure 1) (30,31). This was performed in two ways, using either the region of O 2 response below the GET, S 1 (MRT 1 ), or the total slope S T (MRT T ) (27).…”

Resposta da cinética de consumo de oxigênio e da eficiência mecânica delta de homens e mulheres em diferentes intensidades de esforço

“…The maintenance of the physical exercise depends on a suitable supply of oxygen to the active muscles (6) . The availability of oxygen to the muscle tissue during exercise can be measured through the delta mechanical efficiency (EMr), which corresponds to the quotient between the variation of the energy cost and the variation of the power generated (4,7,8) . In the high intensity exercises the EMr may interfere in the capacity to move high loads of work with predominance of oxidative metabolism, observing extra oxygen consumption (7,8) .…”

“…The availability of oxygen to the muscle tissue during exercise can be measured through the delta mechanical efficiency (EMr), which corresponds to the quotient between the variation of the energy cost and the variation of the power generated (4,7,8) . In the high intensity exercises the EMr may interfere in the capacity to move high loads of work with predominance of oxidative metabolism, observing extra oxygen consumption (7,8) . These observations are not commonly performed with women (8)(9)(10)(11) and the reasons why are unclear, such as: effects of the menstrual cycle and hormone oscillations on the mechanical efficiency.…”

“…In the high intensity exercises the EMr may interfere in the capacity to move high loads of work with predominance of oxidative metabolism, observing extra oxygen consumption (7,8) . These observations are not commonly performed with women (8)(9)(10)(11) and the reasons why are unclear, such as: effects of the menstrual cycle and hormone oscillations on the mechanical efficiency. Lower indices of hemoglobin and hematocrit observed in women can also contribute to the development of anemia (12) , increasing the levels of 2,3 diphospholicerate (2,3-DPG) and hence, decreasing the oxygen affinity with hemoglobin (13,14) .…”