Inter-individual differences in breathing pattern at high levels of incremental cycling exercise in healthy subjects.

Interindividual differences in the rate of changes in tidal volume (V(T)) and respiratory frequency (f(R)) were examined during a maximal incremental cycling exercise. The gain of the inspiratory off-switch reflex was inferred from the V(T) vs. inspiratory duration (T(i)) relationship. Some subjects also executed a static handgrip exercise, used as a "non-dynamic" exercise trial to study patterning of breathing. Above the ventilatory threshold (V(Th)), two patterns of response were identified: in group 1, the rate of change in V(T) significantly increased, while in group 2 the breakpoint of ventilation solely resulted from f(R) increase. After the respiratory compensation point, a tachypnoeic response always occurred. A leftward shift of the V(T) vs. Ti relationship, i.e., an inspiratory off-switch reflex, was measured during the handgrip in group 2 subjects as well as marked f(R) variations. Our study identifies two different patterns of breathing after the V(Th). The subjects who present a tachypnoeic response to exercise above the V(Th) have a higher sensitivity to pulmonary inflation and their tachypnoeic response was ubiquitous during a maximal handgrip test.

Exercise-induced oxidative stress influences the motor control during maximal incremental cycling exercise in healthy humans.

We hypothesized that the changes in blood oxidant/antioxidant status during incremental maximal cycling exercise could affect the motor drive to leg muscles. Indeed, the oxygen free radicals activate the metabosensitive muscle afferents which are suspected to elicit an adaptive motor response delaying fatigue. Fifteen healthy subjects performed an incremental cycling exercise reaching the maximal oxygen uptake (VO2) during which venous blood was repeatedly sampled to measure a marker of lipid peroxidation (TBARS), an antioxidant (reduced ascorbic acid, RAA), and the ischaemia-modified albumin (IMA). The surface EMG of rectus femoris was recorded and the median frequency (MF) of power spectrum was computed. Our main results are: 1) TBARS increased in 7/15 subjects, RAA decreased in 7/15 and IMA increased in 13/15 at VO2max; 4) the MF decrease was correlated to maximal end-exercise IMA increase and RAA decrease. During maximal cycling exercise, the adaptive motor response to cycling closely depends on the magnitude of exercise-induced oxidative stress.