Effects of aging and training status on ventilatory response during incremental cycling exercise.

The aim of this study was to examine the effect of aging and training status on ventilatory response during incremental cycling exercise. Eight young (24 ± 5 years) and 8 older (64 ± 3 years) competitive cyclists together with 8 young (27 ± 4 years) and 8 older (63 ± 2 years) untrained individuals underwent a continuous incremental cycling test to exhaustion to determine ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (VO2max). In addition, the isocapnic buffering (IB) phase was calculated together with the hypocapnic hyperventilation. Ventilatory threshold occurred at similar relative exercise intensities in all groups, whereas RCP was recorded at higher intensities in young and older cyclists compared to the untrained subjects. The IB phase, reported as the difference between VT and RCP and expressed either in absolute (ml·min⁻¹·kg⁻¹ VO2) or in relative terms, was greater (p < 0.01) in both young and older trained cyclists than in untrained subjects, who were also characterized by a lower exercise capacity. Isocapnic buffering was particularly small in the older untrained volunteers. Although young untrained and older trained subjects had a similar level of VO2max, older athletes exhibited a larger IB. In addition, a higher absolute but similar relative IB was observed in young vs. older cyclists, despite a higher VO2max in the former. In conclusion, the present study shows that aging is associated with a reduction of the IB phase recorded during an incremental exercise test. Moreover, endurance training induces adaptations that result in an enlargement of the IB phase independent of age. This information can be used for the characterization and monitoring of the physiological adaptations induced by endurance training.

Neuromuscular and metabolic responses to high-intensity intermittent cycling protocols with different work-to-rest ratios.

PURPOSE: To investigate the effects of work-to-rest-ratio manipulation on neuromuscular and metabolic responses during 2 high-intensity intermittent training (HIT) protocols to exhaustion. Since different exercise durations were expected, the authors hypothesized that the protocol registering a longer duration would have a more pronounced effect on neuromuscular responses, while the other would challenge the cardiopulmonary system more. METHODS: Thirteen competitive cyclists (age 19 ± 2 y) performed a preliminary incremental test to identify their maximal power output and 2 intermittent protocols to exhaustion (40:20s and 30:30s) at a fixed work rate of 135%Pmax interspersed by passive recovery. Surface electromyographic (sEMG) parameters (including muscle-fiber conduction velocity), cardiopulmonary parameters, and blood lactate concentration [La-] were recorded. RESULTS: Time to exhaustion and total work were significantly higher for the 30:30s (38 ± 13 min, 495 ± 161 kJ) than for the 40:20s (10 ± 3 min, 180 ± 51 kJ). No differences were found in sEMG parameters for the 2 protocols. Mean and peak values of VO2, heart rate, ventilatory parameters (except for the peak value of respiratory frequency), and [La-] were significantly higher in the 40:20s than in the 30:30s. CONCLUSIONS: These results do not support the hypothesis that a longer time spent at high intensity has a more pronounced effect on neuromuscular responses, as no differences in EMG parameters were found in the 2 HIT protocols. Regarding metabolic responses, while the 40:20s led to maximal values of VO2, [La-], and ventilatory parameters within a few minutes, the 30:30s allowed maintenance of moderately high values for a considerably longer period, especially for [La-] and ventilatory parameters.

Different effect of cadence on cycling efficiency between young and older cyclists.

PURPOSE: We investigated the difference in the cadence-efficiency relationship between young and older competitive cyclists. METHODS: Eight young (24.3 ± 5.3 yr) and eight older (65.6 ± 2.8 yr) competitive cyclists participated in two laboratory sessions. The first consisted of an incremental maximal cycling test to determine the freely chosen pedal cadence and the maximal power output at VO2max and the second for the determination of gross efficiency (GE), calculated as the ratio of external work and energy expenditure (VO2). The latter test consisted of 6-min cycling exercise bouts at 40% and 60% of maximal power output and at a cadence of 40, 60, 80, 100, and 120 rpm. RESULTS: GE was lower in older cyclists than that in young cyclists at all cadences considered and at both levels of power output (P < 0.01). Peak efficiency was reached at 60 rpm in young cyclists (21.2% ± 1.9%), whereas in older cyclists this was observed already at 40 rpm and was not different from that at 60 rpm (18.3% ± 0.6%). The decline in GE with the increase in cadence was more pronounced in older than in young cyclists (P < 0.01) and was mitigated by the increase in power output more in the latter than in the former. These observations were in line with a lower freely chosen cadence recorded during the maximal test in older than that in young (P < 0.01). CONCLUSIONS: The present data indicate that the effect of cadence on cycling efficiency is different between young and older cyclists and that it seems more disadvantageous for the latter to use high cadences. This may help explain why our older cyclists chose to pedal at lower cadences than the younger.

Non-invasive assessment of muscle fiber conduction velocity during an incremental maximal cycling test.

Muscle fiber conduction velocity (MFCV) gives critical information on neuromuscular control and can be considered a size principle parameter, being suggestive of motor unit recruitment strategies. MFCV has been recently measured during constant-load sub-maximal cycling exercise and was found to correlate positively with percentage of type I myosin heavy chain. The aim of this study was to test the hypothesis that MFCV measured during an incremental cycling test using surface electromyography (sEMG), can be sensitive to the different metabolic requests elicited by the exercise. In particular, the relationship between ventilatory threshold (T-vent), V(')O(2max) and MFCV was explored. Eleven male physically active subjects (age 30+/-9 years) undertook a 1-min incremental cycling test to exhaustion. T-vent and V(')O(2max) were measured using an open circuit breath by breath gas analyzer. The sEMG was recorded from the vastus lateralis muscle with an adhesive 4-electrodes array, and the MFCV was computed on each sEMG burst over the last 30-s of each step. The mean V(')O(2max) obtained during the maximal test was 53.32+/-2.33 ml kg(-1) min(-1), and the T-vent was reached at 80.77+/-3.49% of V(')O(2max). In all subjects reliable measures of MFCV were obtained at every exercise intensity (cross correlation values >0.8). MFCV increased linearly with the mechanical load, reaching a maximum value of 4.28+/-0.67 ms(-1) at an intensity corresponding to the T-vent. Thereafter, MFCV declined until maximal work intensities. This study demonstrates that MFCV can be used as non-invasive tool to infer MUs recruitment/derecruitment strategies even during dynamic exercise from low to maximal intensities.