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

Endurance training improves heart rate on-kinetics in women with subclinical hypothyroidism: a preliminary study

PURPOSE

The aim of the study was to evaluate the effect of endurance training on heart rate (HR) on-kinetics in patients with subclinical hypothyroidism (SH).

METHODS

Eighteen women were randomly assigned to trained group (TG) or control group (CG). Both groups performed three tests at 50 W in a cycle ergometer for 6 min. HR kinetics was obtained during the tests and the mean response time (MRT), which is equivalent to the time taken to reach 63% of the HR at steady state, was extracted. The TG was then submitted to 12 weeks of endurance training (50 min, 3x/week, intensity between 70 and 85% of the maximum HR predicted for the age). Statistical analysis was performed by the mixed analysis of variance.

RESULTS

At baseline, TG and CG were similar for TSH (7.7 ± 3.1 vs. 6.9 ± 3.3 mUI/L, p = 0.602, respectively) and FT4 (12.31 ± 1.51 vs. 12.20 ± 1.89 pmol/L, p = 0.889, respectively). After adjustment for body mass index and age, interactions between moment (baseline or after 12 weeks) and group (trained or control) were only significant for MRT (TG: 39.6 ± 10 to 28.9 ± 8.4 s, CG: 53.6 ± 20.3 to 55 ± 19.7 s, p = 0.001) and physical activity level (CG: 7.3 ± 0.7 to 8 ± 0.9, CG: 6.8 ± 0.8 in both moments, p = 0.005).

CONCLUSION

The preliminary results suggest that 12 weeks of endurance training improve HR on-kinetics and physical activity level in SH.

Confinement, partial sleep deprivation and defined physical activity-influence on cardiorespiratory regulation and capacity

INTRODUCTION

Adequate cardiorespiratory fitness is of utmost importance during spaceflight and should be assessable via moderate work rate intensities, e.g., using kinetics parameters. The combination of restricted sleep, and defined physical exercise during a 45-day simulated space mission is expected to slow heart rate (HR) kinetics without changes in oxygen uptake ([Formula: see text]) kinetics.

METHODS

Overall, 14 crew members (9 males, 5 females, 37 ± 7 yrs, 23.4 ± 3.5 kg m^-2) simulated a 45-d-mission to an asteroid. During the mission, the sleep schedule included 5 nights of 5 h and 2 nights of 8 h sleep. The crew members were tested on a cycle ergometer, using pseudo-random binary sequences, changing between 30 and 80 W on day 8 before (MD-8), day 22 (MD22) and 42 (MD42) after the beginning and day 4 (MD + 4) following the end of the mission. Kinetics information was assessed using the maxima of cross-correlation functions (CCF_max). Higher CCF_max indicates faster responses.

RESULTS

CCF_max(HR) was significantly (p = 0.008) slower at MD-8 (0.30 ± 0.06) compared with MD22 (0.36 ± 0.06), MD42 (0.38 ± 0.06) and MD + 4 (0.35 ± 0.06). Mean HR values during the different work rate steps were higher at MD-8 and MD + 4 compared to MD22 and MD42 (p < 0.001).

DISCUSSION

The physical training during the mission accelerated HR kinetics, but had no impact on mean HR values post mission. Thus, HR kinetics seem to be sensitive to changes in cardiorespiratory fitness and may be a valuable parameter to monitor fitness. Kinetics and capacities adapt independently in response to confinement in combination with defined physical activity and sleep.

Long-lasting exercise involvement protects against decline in V̇O2max and V̇O2 kinetics in moderately active women

We studied the effects of age on different physiological parameters, including those derived from (i) maximal cardiopulmonary exercise testing (CPET), (ii) moderate-intensity step transitions, and (iii) tensiomyography (TMG)-derived variables in moderately active women. Twenty-eight women (age, 19 to 53 years), completed 3 laboratory visits, including baseline data collection, TMG assessment, maximal oxygen uptake test via CPET, and a step-transition test from 20 W to a moderate-intensity cycling power output (PO), corresponding to oxygen uptake at 90% gas exchange threshold. During the step transitions, breath-by-breath pulmonary oxygen uptake, near infrared spectroscopy derived muscle deoxygenation (ΔHHb), and beat-by-beat cardiovascular response were continuously monitored. There were no differences observed between the young and middle-aged women in their maximal oxygen uptake and peak PO, while the maximal heart rate (HR) was 12 bpm lower in middle-aged compared with young (p = 0.016) women. Also, no differences were observed between the age groups in τ pulmonary oxygen uptake, ΔHHb, and τHR during on-transients. The first regression model showed that age did not attenuate the maximal CPET capacity in the studied population (p = 0.638), while in the second model a faster τ pulmonary oxygen uptake, combined with shorter TMG-derived contraction time (Tc) of the vastus lateralis (VL), were associated with a higher maximal oxygen uptake (∼30% of explained variance, p = 0.039). In conclusion, long lasting exercise involvement protects against a maximal oxygen uptake and τpulmonary oxygen uptake deterioration in moderately active women. Novelty: Faster τ pulmonary oxygen uptake and shorter Tc of the VL explain 33% of the variance in superior maximal oxygen uptake attainment. No differences between age groups were found in τ pulmonary oxygen uptake, τΔHHb, and τHR during on-transients.

Cardiovascular regulation: associations between exercise and head-up tilt

It was hypothesized that faster cardiorespiratory kinetics during exercise are associated with higher orthostatic tolerance. Cardiorespiratory kinetics of 14 healthy male subjects (30 ± 4 years, 179 ± 8 cm, 79 ± 8 kg) were tested on a cycle ergometer during exercise with changing work rates of 30 and 80 W. Pulmonary oxygen uptake ( ) was measured breath-by-breath and heart rate (HR), mean arterial blood pressure (MAP), and total peripheral resistance (TPR) were measured beat-to-beat. Muscular oxygen uptake ( ) was estimated from HR and . Kinetic parameters were determined by time-series analysis, using cross-correlation functions (CCF_max(x)) between the parameter and the work rate. Cardiovascular regulations of MAP, HR, and TPR during orthostatic stress were measured beat-to-beat on a tilt seat. Changes between the minima and maxima during the 6° head-down tilt and the 90° head-up tilt positions were calculated for each parameter (Δ_tilt-up). correlated significantly with ΔTPR_tilt-up (r = 0.790, p ≤ 0.001). CCF_max(HR) was significantly correlated with ΔHR_tilt-up (r = -0.705, p = 0.002) and the amplitude in HR from 30 to 80 W (r_SP = -0.574, p = 0.016). The observed correlations between cardiorespiratory regulation in response to exercise and orthostatic stress during rest might allow for a more differential analysis of the underlying mechanisms of orthostatic intolerance in, for example, patient groups.

Gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise

PURPOSE

To evaluate the effects of exercise velocity (60, 150, 240deg∙s^-1) and muscle mass (arm vs leg) on changes in gas exchange and arterio-venous oxygen content difference (avDO₂) following high-intensity concentric-eccentric isokinetic exercise.

METHODS

Fourteen subjects (26.9±3.1years) performed a 3×20-repetition isokinetic exercise protocol. Recovery beat-to-beat cardiac output (CO) and breath-by-breath gas exchange were recorded to determine post-exercise half-time (t_1/2) for oxygen uptake (V˙O₂pulm), carbon dioxide output (V˙CO₂pulm), and ventilation (V˙_E).

RESULTS

Significant differences of the t_1/2 values were identified between 60 and 150deg∙s^-1. Significant differences in the t_1/2 values were observed between V˙O₂pulm and V˙CO₂pulm and between V˙CO₂pulm and V˙_E. The time to attain the first avDO₂-peak showed significant differences between arm and leg exercise.

CONCLUSIONS

The present study illustrates, that V˙O₂pulm kinetics are distorted due to non-linear CO dynamics. Therefore, it has to be taken into account, that V˙O₂pulm may not be a valuable surrogate for muscular oxygen uptake kinetics in the recovery phases.