Early effects of exercise training on $\mathop V\limits^ \cdot {\rm O}_2$ on- and off-kinetics in 50-year-old subjects

Abstract.

We tested the hypothesis that, in healthy middle-aged subjects (n=11, age 51.0±3.0 years, x ±SD), the effects of exercise training on pulmonary O₂ uptake ($\dot VO_2$ ) on- and off-kinetics would appear earlier than those on peak $\mathop V\limits^ \cdot {\rm O}_2$ . The subjects underwent a standard training program (combined endurance and resistance training) in a health club, and were evaluated before training ("time 0", T0), and after 7 (T7), 15 (T15), 30 (T30), 60 (T60) and 90 (T90) days of training. Breath-by-breath pulmonary O₂ uptake ($\dot VO_2$ ), heart rate (HR), systolic (SBP) and diastolic blood pressure, and capillary blood lactate concentration ([La]_b) were determined at rest and at each workload ($\dot w$ during a cycle ergometer incremental exercise test. The "heart rate · blood pressure product" was calculated as (HR·SBP). The day following the incremental test, the subjects performed three repetitions of a square-wave exercise at 50% of $\mathop V\limits^ \cdot {\rm O}_2 _{{\rm peak}}$ , for the determination of pulmonary $\mathop V\limits^ \cdot {\rm O}_2$ on- and off-kinetics. $\mathop V\limits^ \cdot {\rm O}_2 _{{\rm peak}}$ and [La]_bpeak tended to increase with training; the increases became significant at T60 or T90. HR_peak and (HR·SBP)_peak were unaffected by training. The time constant of the "primary" component of the $\mathop V\limits^ \cdot {\rm O}_2$ on-kinetics (τ₂) was 46.9±17.3 s (T0), 38.1±14.2 s (T7), 34.4±12.6 s (T15), 28.8±6.8 s (T30), 30.2±8.0 s (T60), and 30.4±12.4 s (T90); a significant difference compared to T0 was observed from T15 onward. From T15 onward, τ₂ were not significantly different from values obtained (29.2±5.3 s) from a group of healthy untrained young controls (n=7, 21.6±0.5 years). The same pattern of change as a function of training was described for the $\mathop V\limits^ \cdot {\rm O}_2$ off-kinetics. It is concluded that in 50-year-old subjects $\mathop V\limits^ \cdot {\rm O}_2$ on- and off-kinetics are more sensitive to exercise training than other physiological variables determined at peak exercise.