The sustainability of VO2max: effect of decreasing the workload.

The study examined the maintenance of VO(2max) using VO(2max) as the controlling variable instead of power. Therefore, ten subjects performed three exhaustive cycling exercise bouts: (1) an incremental test to determine VO(2max) and the minimal power at VO(2max) (PVO(max)), (2) a constant-power test at PVO(max) and (3) a variable-power test (VPT) during which power was varied to control VO(2) at VO(2max). Stroke volume (SV) was measured by impedance in each test and the stroke volume reserve was calculated as the difference between the maximal and the average 5-s SV. Average power during VPT was significantly lower than PVO(max) (238 ± 79 vs. 305 ± 86 W; p < 0.0001). All subjects, regardless of their VO(2max) values and/or their ability to achieve a VO(2max) plateau during incremental test, were able to sustain VO(2max) for a significantly longer time during VPT compared to constant-power test (CPT) (958 ± 368 s vs. 136 ± 81 s; p < 0.0001). Time to exhaustion at VO(2max) during VPT was correlated with the power drop in the first quarter of the time to exhaustion at VO(2max) (r = 0.71; p < 0.02) and with the stroke volume reserve (r = 0.70, p = 0.02) but was not correlated with VO(2max). This protocol, using VO(2max) rather than power as the controlling variable, demonstrates that the maintenance of exercise at VO(2max) can exceed 15 min independent of the VO(2max) value, suggesting that the ability to sustain exercise at VO(2max) has different limiting factors than those related to the VO(2max) value.

Steering behaviour can be modulated by different optic flows during walking.

Optic flow is a typical pattern of visual motion that can be used to control locomotion. While the ability to discriminate translational or rotational optic flows have been extensively studied, how these flows control steering during locomotion is not known. The goal of this study was to compare the steering behaviour of subjects subjected to rotational, translational, or combined (rotational added to translational) optic flows with a focus of expansion (FOE) located to the right, left, or straight ahead. Ten healthy young subjects were instructed to walk straight in a virtual room viewed through a helmet mounted display while the location of the FOE was randomly offset. Horizontal trajectory of the body's centre of mass (CoM), as well as rotations of the head, trunk and foot were recorded in coordinates of both the physical and virtual worlds. Results show that subjects experienced a mediolateral shift in CoM opposite to the FOE location, with larger corrections being observed at more eccentric FOE locations. Head and body segment reorientations were only observed for optic flows containing a rotational component. CoM trajectory corrections in the physical world were also of small magnitude, leading to deviation errors in the virtual world. Altogether, these results suggest a profound influence of vision, especially due to the pattern of visual motion, on steering behaviours during locomotion.