The respiratory Vco2/Vo2 exchange ratio during maximum exercise and its use as a predictor of maximum oxygen uptake

Effect of Cardiorespiratory Fitness on Verifying VO2max in Middle-aged and Older Adults

We investigated the effect of cardiorespiratory fitness (CRF) on the probability of achieving the verification criterion to confirm that VO₂max was obtained in a sample of middle-aged to older adults. Data from twelve men and nine women (60.7±8.5 years, VO₂max: 34.8±9.4 mL/kg/min) were used for analysis. Participants had their VO₂max measured via a maximal graded exercise test and confirmed using a verification bout on a cycle ergometer. Logistic regression was used to evaluate the effect of CRF (VO₂max) on the probability a participant would successfully achieve the verification criterion. Odds ratios are reported to quantify the effect size. No statistically significant relationship was observed between CRF and achieving the verification criterion (β=.081, SE=.0619, Wald=1.420, p=.156). Estimated odds ratio for the effect of CRF on the verification criterion indicated an increase of 8% [Exp(β)=1.08, 95% CI (0.96, 1.22)] in the probability of achieving the verification criterion given a one unit increase in VO₂max. Each 1 mL/kg/min increase in VO₂max results in an 8% increase in the chance that an individual achieves the verification criterion confirming that VO₂max was obtained. Therefore, CRF is likely of practical significance and should be considered when deciding to use a verification trial.

Can linear regression confirm VO2max was attained in middle-aged and older adults?

PURPOSE

Evaluate the efficacy of a regression method for identifying a VO₂ plateau to confirm the attainment of VO₂max compared to a verification trial in middle-aged and older adults.

METHODS

Eleven men and ten women (age 61.0 ± 8.1, VO₂max 21.8-50.3 ml/kg/min, n = 21) completed an individualized ramp graded exercise test (GXT) on the cycle ergometer, and one hour later, a verification trial at 105% of their maximal work rate (WR) achieved during the GXT. A plateau in VO₂ was used to confirm VO₂max was attained. VO₂ plateau was identified using the difference between the highest VO₂ between the two trials and a linear regression analysis of the VO₂-WR relationship during the GXT. McNemar's test of marginal homogeneity was used to detect differences in the proportion of paired data of individuals' attainment of VO₂max criteria.

RESULTS

Of the 21 participants, 15 (71.4%) met the verification criterion while 6 (28.6%) did not, compared to the regression method where 16 (76.2%) achieved the regression criterion while 5 (23.8%) did not. McNemar's test revealed no significant difference between participants' ability to achieve the regression and verification criteria (p = 0.999).

CONCLUSION

The regression method is an effective strategy for confirming VO₂max was attained with middle-aged and older adults on a cycle ergometer. This time-efficient regression method is comparable with the verification criterion but does not require a second maximal test, which may be advantageous for those where the verification trial may not be practical.

Does heart rate response confirm the attainment of maximal oxygen uptake in adults 45 years and older?

PURPOSE

To test the efficacy of a plateau in heart rate (HR_plat) as an effective indicator for confirming [Formula: see text]max attainment in a middle-aged to older sample.

METHODS

Nine men and eleven women (age 60 ± 8.5 years, [Formula: see text]max 35.9 ± 9.4 ml/kg/min, N = 20) completed a single [Formula: see text]max test on both the treadmill and cycle ergometer.[Formula: see text]max was confirmed using a plateau in [Formula: see text] ([Formula: see text]_plat) of ≤ 150 ml/min, a verification bout, and HR_plat (≤ 4 bpm).

RESULTS

[Formula: see text]_plat occurred in 100% and 95% of participants on the treadmill and cycle ergometer, respectively. Verification criteria ([Formula: see text]max during verification ≤ 2% of [Formula: see text]max during incremental test) were met by 80% of participants on both modalities. HR_plat was achieved by 90% and 70% of participants on the treadmill and cycle ergometer, respectively.

CONCLUSION

These results suggest that a verification bout is reliable for confirming [Formula: see text]max in older adults on both modalities. In our sample of middle-aged and older adults, [Formula: see text]_plat was the most robust method to assess [Formula: see text]max when indirect calorimetry is available. Although more research is warranted, when indirect calorimetry is not available, a HR_plat of ≤ 4 bpm may be a useful alternative to get an accurate representation of maximal effort in middle-aged and older adults.

Different times of day do not change heart rate variability recovery after light exercise in sedentary subjects: 24 hours Holter monitoring

Incidence of cardiovascular events follows a circadian rhythm with peak occurrence during morning. Disturbance of autonomic control caused by exercise had raised the question of the safety in morning exercise and its recovery. Furthermore, we sought to investigate whether light aerobic exercise performed at night would increase HR and decrease HRV during sleep. Therefore, the aim of this study was to test the hypothesis that morning exercise would delay HR and HRV recovery after light aerobic exercise, additionally, we tested the impact of late night light aerobic exercise on HR and HRV during sleep in sedentary subjects. Nine sedentary healthy men (age 24 ± 3 yr; height 180 ± 5 cm; weight 79 ± 8 kg; fat 12 ± 3%; mean±SD) performed 35 min of cycling exercise, at an intensity of first anaerobic threshold, at three times of day (7 a.m., 2 p.m. and 11 p.m.). R-R intervals were recorded during exercise and during short-time (60 min) and long-time recovery (24 hours) after cycling exercise. Exercise evoked increase in HR and decrease in HRV, and different times of day did not change the magnitude (p < 0.05 for time). Morning exercise did not delay exercise recovery, HR was similar to rest after 15 minutes recovery and HRV was similar to rest after 30 minutes recovery at morning, afternoon, and night. Low frequency power (LF) in normalized unites (n.u.) decreased during recovery when compared to exercise, but was still above resting values after 60 minutes of recovery. High frequency power (HF-n.u.) increased after exercise cessation (p < 0.05 for time) and was still below resting values after 60 minutes of recovery. The LF/HF ratio decreased after exercise cessation (p < 0.05 for time), but was still different to baseline levels after 60 minutes of recovery. In conclusion, morning exercise did not delay HR and HRV recovery after light aerobic cycling exercise in sedentary subjects. Additionally, exercise performed in the night did change autonomic control during the sleep. So, it seems that sedentary subjects can engage physical activity at any time of day without higher risk.

Faster heart rate and muscular oxygen uptake kinetics in type 2 diabetes patients following endurance training

Cardiorespiratory kinetics were analyzed in type 2 diabetes patients before and after a 12-week endurance exercise-training intervention. It was hypothesized that muscular oxygen uptake and heart rate (HR) kinetics would be faster after the training intervention and that this would be detectable using a standardized work rate protocol with pseudo-random binary sequences. The cardiorespiratory kinetics of 13 male sedentary, middle-aged, overweight type 2 diabetes patients (age, 60 ± 8 years; body mass index, 33 ± 4 kg·m^-2) were tested before and after the 12-week exercise intervention. Subjects performed endurance training 3 times a week on nonconsecutive days. Pseudo-random binary sequences exercise protocols in combination with time series analysis were used to estimate kinetics. Greater maxima in cross-correlation functions (CCF_max) represent faster kinetics of the respective parameter. CCF_max of muscular oxygen uptake (pre-training: 0.31 ± 0.03; post-training: 0.37 ± 0.1, P = 0.024) and CCF_max of HR (pre-training: 0.25 ± 0.04; post-training: 0.29 ± 0.06, P = 0.007) as well as peak oxygen uptake (pre-training: 24.4 ± 4.7 mL·kg^-1·min^-1; post-training: 29.3 ± 6.5 mL·kg^-1·min^-1, P = 0.004) increased significantly over the course of the exercise intervention. In conclusion, kinetic responses to changing work rates in the moderate-intensity range are similar to metabolic demands occurring in everyday habitual activities. Moderate endurance training accelerated the kinetic responses of HR and muscular oxygen uptake. Furthermore, the applicability of the used method to detect these accelerations was demonstrated.

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

This study examined the effects of dietary manipulation upon the respiratory exchange ratio (R = VCO2/VO2) as a predictor of maximum oxygen uptake (VO2max). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45 +/- 5% carbohydrate (CHO] for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3 +/- 2% CHO), and again after three days of a high CHO diet (61 +/- 5% CHO). Respiratory gases were continuously monitored during each test using an on-line system. No significant changes in mean exercise oxygen uptake (VO2), VO2max or maximum functional heart rate (FHRmax) were found between tests. Mean exercise carbon dioxide output (VCO2) and R were significantly lower than normal after the low CHO diet (both p less than 0.001) and significantly higher than normal after the high CHO diet (both p less than 0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p less than 0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p less than 0.05) over the final 5 min of exercise, after the high CHO diet.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of high intensity training upon respiratory gas exchanges during fixed term maximal incremental exercise in man

The response of respiratory gas exchanges to a 6 week high intensity training program was examined in 5 healthy males during fixed term maximal incremental treadmill exercise. Training was performed 3 d.wk-1 and consisted of a progressive series of repeated 15 sec and 30 sec maximal runs, and weight training exercises for the leg extensor muscles. Respiratory gases during the tests were continuously monitored using an on-line system. Muscle biopsy samples were obtained from the m. vastus lateralis before and after training for histochemical determination of fibre distribution based on myosin ATP-ase activity, and fibre cross-sectional area based on NADH-Tetrazolium Reductase activity. Training significantly increased the proportion of type IIa fibres (+5.9 +/- 2.0%, p less than 0.001) and decreased type I fibres (-6.3 +/- 2.0%, p less than 0.001), the distribution of type IIb fibres remained unchanged (+0.4 +/- 0.9%). Muscle cross-sectional area also showed a significant increase after training in type I (+318 +/- 215 microns 2, p less than 0.05), IIa (+652 +/- 207 microns 2, p less than 0.001) and IIb (+773 +/- 196 microns 2, p less than 0.001) fibres. During fixed term maximal incremental exercise the mean carbon dioxide output (VCO2) and mean respiratory exchange ratio (R = VCO2/VO2) were significantly increased (p less than 0.01) after training. The R-time relationship was at all times shifted to the left after training, being significantly (p less than 0.01) so over the final five min of exercise. No changes in mean exercise oxygen uptake (VO2), maximum oxygen uptake (VO2max) and maximum heart rate (FHRmax) were observed between tests.(ABSTRACT TRUNCATED AT 250 WORDS)