Influence of Age on Cardiorespiratory Kinetics During Sinusoidal Walking in Humans

We sought to determine the influence of age on cardiorespiratory kinetics during sinusoidal walking in two groups: 13 healthy young subjects (YG; 7 men and 6 women, age 21 ± 2 years) and 15 healthy elderly subjects (ELD; 9 men and 6 women, age 67 ± 5 years). A treadmill’s speed was sinusoidally changed between 3 and 6 km h-1 in the YG and between 3 and 5 km h-1 in the ELD during periods of 1, 2, 5, and 10 min, and in a stepwise manner. We compared the groups’ heart rate (HR), ventilation (V˙E), and gas exchange (CO2 output (V˙CO2) and O2 uptake (V˙O2)) responses. We determined the phase shift (PS) and the normalized amplitude (Amp) ratio of these kinetics in relation to the sinusoidal change in walking speed in response to the magnitude from the maximum to minimum speeds as revealed by a Fourier analysis in all cardiorespiratory variables. Both the Amp ratio and PS in the V˙E, V˙CO2, and V˙O2 responses were very similar between the ELD and YG, and being independent of the periods of sinusoidal oscillations. In marked contrast, the PS of the HR kinetics was significantly slowed in the ELD compared to the YG. The Amp ratio of HR was not related to the covariance variation of HR (CVHR) at standing rest in the ELD. The HR kinetics during sinusoidal walking may not be attributable to parasympathetic nerve activity into the heart in the ELD. The slope of the Amp of V˙E related to the Amp of V˙CO2 (V˙E/V˙CO2 slope) was steeper in the ELD (0.0258) compared to the YG (0.0132), suggesting that exercise hyperpnea could be greatly induced during walking in the ELD. These findings suggest that aging influences the alterations of autonomic nervous system-dependent slower HR kinetics and exercise hyperpnea during walking in the ELD

Alterations in step frequency and muscle activities using body weight support influence the ventilatory response to sinusoidal walking in humans

Abstract The use of body weight support (BWS) can reveal important insights into the relationship between lower-limb muscle activities and the ventilatory response during sinusoidal walking. Here, healthy participants (n = 15) walked on a treadmill while 0%, 30%, and 50% of their body weight was supported with BWS. The walking speed was varied sinusoidally between 3 and 6 km h−1, and three different frequencies, and periods ranging from 2 to 10 min were used. Breath-by-breath ventilation ( $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E ) and CO2 output ( $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 ) were measured. The tibialis anterior (TA) muscle activity was measured by electromyography throughout the walking. The amplitude (Amp), normalized Amp [Amp ratio (%)], and phase shift (PS) of the sinusoidal variations in measurement variables were calculated using a Fourier analysis. The results revealed that the Amp ratio in $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E increased with the increase in BWS. A steeper slope of the $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E – $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 relationship and greater $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E / $${\dot{\text{V}}}\text{CO}_{{2}}$$ V ˙ CO 2 values were observed under reduced body weight conditions. The Amp ratio in TA muscle was significantly positively associated with the Amp ratio in the $${\dot{\text{V}}}_{{\text{E}}}$$ V ˙ E (p < 0.001). These findings indicate that the greater amplitude in the TA muscle under BWS may have been a potent stimulus for the greater response of ventilation during sinusoidal walking

Effects of a water-soluble phytostanol ester on plasma cholesterol levels and red blood cell fragility in hamsters

Peer reviewed: YesNRC publication: Ye

Differential kinetics of the cardiac, ventilatory, and gas exchange variables during walking under moderate hypoxia

<div><p>We investigated the effects of moderate hypoxia (FiO₂ = 15%) on different kinetics between pulmonary ventilation () and heart rate (HR) during treadmill walking. <i>Breath-by-breath</i> , oxygen uptake (), carbon dioxide output (), and HR were measured in 13 healthy young adults. The treadmill speed was sinusoidally changed from 3 to 6 km·h^-1 with four oscillation periods of 1, 2, 5, and 10 min. The amplitude (<i>Amp</i>), phase shift (<i>PS</i>) and mean values of these kinetics were obtained by harmonic analysis. The mean values of all of these responses during walking at a sinusoidally changing speed became greater under hypoxia compared to normoxia (FiO₂ = 21%), indicating that moderate hypoxia could achieve an increased energy expenditure (increased and ) and hyperventilation. The <i>Amp</i> values of the , , and kinetics were not significantly different between normoxia and hypoxia at most periods, although a significantly smaller <i>Amp</i> of the HR was observed at faster oscillation periods (1 or 2 min).The <i>PS</i> of the HR was significantly greater under hypoxia than normoxia at the 2, 5, and 10 min periods, whereas the <i>PS</i> of the , , and responses was not significantly different between normoxia and hypoxia at any period. These findings suggest that the lesser changes in <i>Amp</i> and <i>PS</i> in ventilatory and gas exchange kinetics during walking at a sinusoidally changing speed were remarkably different from a deceleration in HR kinetics under moderate hypoxia.</p></div

Application of Molecular Hydrogen as an Antioxidant in Responses to Ventilatory and Ergogenic Adjustments during Incremental Exercise in Humans

We investigated effects of molecular hydrogen (H2) supplementation on acid-base status, pulmonary gas exchange responses, and local muscle oxygenation during incremental exercise. Eighteen healthy, trained subjects in a randomized, double-blind, crossover design received H2-rich calcium powder (HCP) (1500 mg/day, containing 2.544 µg/day of H2) or H2-depleted placebo (1500 mg/day) for three consecutive days. They performed cycling incremental exercise starting at 20-watt work rate, increasing by 20 watts/2 min until exhaustion. Breath-by-breath pulmonary ventilation (V˙E) and CO2 output (V˙CO2) were measured and muscle deoxygenation (deoxy[Hb + Mb]) was determined via time-resolved near-infrared spectroscopy in the vastus lateralis (VL) and rectus femoris (RF). Blood gases’ pH, lactate, and bicarbonate (HCO3−) concentrations were measured at rest and 120-, 200-, and 240-watt work rates. At rest, the HCP group had significantly lower V˙E, V˙CO2, and higher HCO3−, partial pressures of CO2 (PCO2) versus placebo. During exercise, a significant pH decrease and greater HCO3− continued until 240-watt workload in HCP. The V˙E was significantly lower in HCP versus placebo, but HCP did not affect the gas exchange status of V˙CO2 or oxygen uptake (V˙O2). HCP increased absolute values of deoxy[Hb + Mb] at the RF but not VL. Thus, HCP-induced hypoventilation would lead to lower pH and secondarily impaired balance between O2 delivery and utilization in the local RF during exercise, suggesting that HCP supplementation, which increases the at-rest antioxidant potential, affects the lower ventilation and pH status during incremental exercise. HPC induced a significantly lower O2 delivery/utilization ratio in the RF but not the VL, which may be because these regions possess inherently different vascular/metabolic control properties, perhaps related to fiber-type composition

Time course of the ventilatory and gas exchange responses at different periods.

<p>The responses of a representative subject’s variables of ventilation (), O₂ uptake (), CO₂ output (), heart rate (HR), tidal volume (VT), and breath frequency (B<i>f</i>) over four different periods of 1, 2, 5, and 10 min are shown. Oscillating lines: Superimposed data on gas exchange variable. <i>Smooth lines</i>: Fundamental sine-wave component of these kinetics.</p

Effects of different phytosterol analogs on colonic mucosal cell proliferation in hamsters

Peer reviewed: YesNRC publication: Ye

Energy expenditure, body composition and maximal oxygen uptake in middle-aged Japanese women who have long-term habits of exercising

[[abstract]]The purpose of this study was to examine the effects of long-term habitual exercise on daily total energy expenditure (TEE) and its components, body composition and maximal oxygen uptake (VO2max) in middle-aged Japanese women. Twenty-eight subjects aged 39 to 58 years were assigned either to a nonhabitual exercise group (Control ; n=12) or a habitual exercise group (Exercise ; n=16). TEE, physical activity level (PAL) and the daily physical activity energy expenditure (PAEE) were assessed by doubly labeled water (DLW) method. The exercise-induced energy expenditure (ExEE) and nonexercise-induced energy expenditure (NExEE) were evaluated based on the activity record investigation conducted simultaneously during the DLW measurement period. The result follows that TEE was significantly (p<0.01) higher in the Exercise group (2520 kcal · day-1) than in the Control group (1921 kcal · day-1). There was no significant difference in basal metabolic rate between the groups. PAEE and ExEE were significantly higher in the Exercise group than in the Control group (p<0.01). Habitual exercise induced an increase in TEE without resulting in a compensatory reduction of NExEE. The percentage body fat (fat%) was significantly lower in the Exercise group (25.5%) than in the Control group (30.9%). VO2max was higher in the Exercise group (1788 ml · min-1) than in the Control group (1417 ml. min-1). After correction for body weight, fat% was negatively associated with TEE (p<0.01), PAEE (p<0.01) and ExEE (p=0.05), while VO2max was positively associated with TEE (p<0.05), PAL (p<0.05), PAEE (p<0.05) and ExEE (p<0.01). These results suggest that habitual exercise is associated with the increase of TEE, the improvement of body composition and VO2max. The improvement of VO2max was mainly caused by the increase in ExEE, indicating that the exercise intensity is important to the improvement of cardiorespiratory endurance fitness

Comparison of the <i>Amp</i> and <i>PS</i> of HR kinetics between hypoxia and normoxia.

<p>Differences in the dynamic responses of a representative subject’s HR between normoxia and hypoxia at the representative sinusoidal period of 5 min are shown (<b>A</b>). The <i>Mx</i> (<b>B</b>), <i>Amp</i> (<b>C</b>), and <i>PS</i> (<b>D</b>) are shown for hypoxia (blue lines) and normoxia (red lines) as a function of the periods of the sinusoidal changes in the treadmill speed. *p < 0.05, **p < 0.01, ***p < 0.001 for hypoxia vs. normoxia. Data are means ± SD.</p