Observational study OBJECTIVE: To investigate the effects of prolonged arm-crank exercise on cardiovascular drift (CV
) in spinal cord injury (SCI).
This is a community-based supervision study ...METHODS: Ten participants with motor -complete or incomplete SCI (lesion level T7-L1), and 10 able-bodied (AB) participants matched for age performed a 40-min arm-crank exercise at an intensity of 50% of peak oxygen uptake (VO
).
During the exercise, there were no significant differences between the groups in VO
, tissue O
saturation in the biceps brachii (active muscle), and chest and arm skin temperature (all P > 0.05). In the AB, heart rate (HR) increased within the first 15 min of the exercise and continued to increase until the end of the exercise; however, in the SCI, HR increased within first 15 min of the exercise and then remained constant until the end of exercise. After 10 min of exercise, thigh skin temperature had increased more in the SCI than in the AB (P < 0.05). Thigh skin blood flow (SkBF) continued to increase after 10 min of exercise in the AB but remained almost stable in the SCI. Relative changes in the thigh SkBF were associated with changes in HR during exercise between the values at 10 min and 40 min in the pooled data (R
= 0.706, P < 0.001).
CV
during the prolonged arm-crank exercise was not observed in individuals with SCI. This might be partially explained by different responses in cutaneous circulation within the inactive muscles of these participants.
Energy expenditure (EE) during treadmill walking under normal conditions (normobaric normoxia, 21% O
) and moderate hypoxia (13% O
) was measured. Ten healthy young men and ten healthy young women ...walked on a level (0°) gradient a range of speeds (0.67-1.67 m s
). During walking, there were no significant differences in reductions in arterial oxygen saturation (SpO
) between the sexes. The hypoxia-induced increase in EE, heart rate (HR bpm) and ventilation (Formula: see text L min
) were calculated. Using a multivariate model that combined EE, Formula: see text, and HR to predict ΔSpO
(hypoxia-induced reduction), a very strong fit model both for men (r
= 0.900, P < 0.001) and for women was obtained (r
= 0.957, P < 0.001). The contributions of EE, VE, and HR to ΔSpO
were markedly different between men and women. Formula: see text and EE had a stronger effect on ΔSpO
in women (Formula: see text: 4.1% in women vs. 1.7% in men; EE: 28.1% in women vs. 15.8% in men), while HR had a greater effect in men (82.5% in men and 67.9% in women). These findings suggested that high-altitude adaptation in response to hypoxemia has different underlying mechanisms between men and women. These results can help to explain how to adapt high-altitude for men and women, respectively.
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 CO
2
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.
Purpose
We tested the hypothesis that incremental ramp cycling exercise performed in the supine position (
S
) would be associated with an increased reliance on muscle deoxygenation (deoxyheme) in ...the deep and superficial
vastus lateralis
(VLd and VLs, respectively) and the superficial
rectus femoris
(RFs) when compared to the upright position (
U
).
Methods
11 healthy men completed ramp incremental exercise tests in
S
and
U
. Pulmonary
V
˙
O
2
was measured breath-by-breath; deoxyheme was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs.
Results
Supine exercise increased the overall change in deoxyheme from baseline to maximal exercise in the VLs (
S
: 38 ± 23 vs.
U
: 26 ± 15 μM,
P
< 0.001) and RFs (
S
: 36 ± 21 vs.
U
: 25 ± 15 μM,
P
< 0.001), but not in the VLd (
S
: 32 ± 23 vs.
U
: 29 ± 26 μM,
P
> 0.05).
Conclusions
The present study supports that the impaired balance between O
2
delivery and O
2
utilization observed during supine exercise is a regional phenomenon within superficial muscles. Thus, deep muscle defended its O
2
delivery/utilization balance against the supine-induced reductions in perfusion pressure. The differential responses of these muscle regions may be explained by a regional heterogeneity of vascular and metabolic control properties, perhaps related to fiber type composition.
The oxygen cost of transport per unit distance (CoT; mL·kg(-1)·km(-1)) shows a U-shaped curve as a function of walking speed (v), which includes a particular walking speed minimizing the CoT, so ...called economical speed (ES). The CoT-v relationship in running is approximately linear. These distinctive walking and running CoT-v relationships give an intersection between U-shaped and linear CoT relationships, termed the energetically optimal transition speed (EOTS). This study investigated the effects of subtracting the standing oxygen cost for calculating the CoT and its relevant effects on the ES and EOTS at the level and gradient slopes (±5%) in eleven male trained athletes. The percent effects of subtracting the standing oxygen cost (4.8 ± 0.4 mL·kg(-1)·min(-1)) on the CoT were significantly greater as the walking speed was slower, but it was not significant at faster running speeds over 9.4 km·h(-1). The percent effect was significantly dependent on the gradient (downhill > level > uphill, P < 0.001). The net ES (level 4.09 ± 0.31, uphill 4.22 ± 0.37, and downhill 4.16 ± 0.44 km·h(-1)) was approximately 20% slower than the gross ES (level 5.15 ± 0.18, uphill 5.27 ± 0.20, and downhill 5.37 ± 0.22 km·h(-1), P < 0.001). Both net and gross ES were not significantly dependent on the gradient. In contrast, the gross EOTS was slower than the net EOTS at the level (7.49 ± 0.32 vs. 7.63 ± 0.36 km·h(-1), P = 0.003) and downhill gradients (7.78 ± 0.33 vs. 8.01 ± 0.41 km·h(-1), P < 0.001), but not at the uphill gradient (7.55 ± 0.37 vs. 7.63 ± 0.51 km·h(-1), P = 0.080). Note that those percent differences were less than 2.9%. Given these results, a subtraction of the standing oxygen cost should be carefully considered depending on the purpose of each study.
We investigated the effects of moderate hypoxia (FiO2 = 15%) on different kinetics between pulmonary ventilation (Formula: see text) and heart rate (HR) during treadmill walking. Breath-by-breath ...Formula: see text, oxygen uptake (Formula: see text), carbon dioxide output (Formula: see text), 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 (Amp), phase shift (PS) 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 Formula: see text and Formula: see text) and hyperventilation. The Amp values of the Formula: see text, Formula: see text, and Formula: see text kinetics were not significantly different between normoxia and hypoxia at most periods, although a significantly smaller Amp of the HR was observed at faster oscillation periods (1 or 2 min).The PS of the HR was significantly greater under hypoxia than normoxia at the 2, 5, and 10 min periods, whereas the PS of the Formula: see text, Formula: see text, and Formula: see text responses was not significantly different between normoxia and hypoxia at any period. These findings suggest that the lesser changes in Amp and PS 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.
Energy cost of transport per unit distance (CoT; J·kg-1·km-1) displays a U-shaped fashion in walking and a linear fashion in running as a function of gait speed (v; km·h-1). There exists an ...intersection between U-shaped and linear CoT-v relationships, being termed energetically optimal transition speed (EOTS; km·h-1). Combined effects of gradient and moderate normobaric hypoxia (15.0% O2) were investigated when walking and running at the EOTS in fifteen young males. The CoT values were determined at eight walking speeds (2.4-7.3 km·h-1) and four running speeds (7.3-9.4 km·h-1) on level and gradient slopes (±5%) at normoxia and hypoxia. Since an alteration of tibialis anterior (TA) activity has been known as a trigger for gait transition, electromyogram was recorded from TA and its antagonists (gastrocnemius medialis (GM) and gastrocnemius lateralis (GL)) for about 30 steps during walking and running corresponding to the individual EOTS in each experimental condition. Mean power frequency (MPF; Hz) of each muscle was quantified to evaluate alterations of muscle fiber recruitment pattern. The EOTS was not significantly different between normoxia and hypoxia on any slopes (ranging from 7.412 to 7.679 km·h-1 at normoxia and 7.516 to 7.678 km·h-1 at hypoxia) due to upward shifts (enhanced metabolic rate) of both U-shaped and linear CoT-v relationships at hypoxia. GM, but not GL, activated more when switching from walking to running on level and gentle downhill slopes. Significant decreases in the muscular activity and/or MPF were observed only in the TA when switching the gait pattern. Taken together, the EOTS was not slowed by moderate hypoxia in the population of this study. Muscular activities of lower leg extremities and those muscle fiber recruitment patterns are dependent on the gradient when walking and running at the EOTS.
Several factors have been shown to contribute to hypoxic-induced declined in aerobic capacity. In the present study, we investigated the effects of resting hypoxic ventilatory and cardiac responses ...(HVR and HCR) on hypoxic-induced declines in peak oxygen uptake (formula omittedO.sub.2peak). Peak oxygen uptakes was measured in normobaric normoxia (room air) and hypoxia (14.1% O.sub.2) for 10 young healthy men. The resting HVR and HCR were evaluated at multiple steps of hypoxia (1 h at each of 21, 18, 15 and 12% O.sub.2). Arterial desaturation (DELASaO.sub.2) was calculate by the difference between SaO.sub.2 at normoxia--at each level of hypoxia (%). HVR was calculate by differences in pulmonary ventilation between normoxia and each level of hypoxia against DELASaO.sub.2 (L min.sup.-1 %.sup.-1 kg.sup.-1). Similarly, HCR was calculated by differences in heart rate between normoxia and each level of hypoxia against DELASaO.sub.2 (beats min.sup.-1 %.sup.-1). formula omittedO.sub.2peak significantly decreased in hypoxia by 21% on average (P < 0.001). HVR was not associated with changes in formula omittedO.sub.2peak. DELASaO.sub.2 from normoxia to 18% or 15% O.sub.2 and HCR between normoxia and 12% O.sub.2 were associated with changes in formula omittedO.sub.2peak (P < 0.05, respectively). The most optimal model using multiple linear regression analysis found that DELAHCR at 12% O.sub.2 and DELASaO.sub.2 at 15% O.sub.2 were explanatory variables (adjusted R.sup.2 = 0.580, P = 0.02). These results suggest that arterial desaturation at moderate hypoxia and heart rate responses at severe hypoxia may account for hypoxic-induced declines in peak aerobic capacity, but ventilatory responses may be unrelated.
Since walking is a daily activity not to require the maximal effort in healthy populations, a very few universal bio-parameters and/or methods have been defined to evaluate individual walking ...characteristics in those populations. A concept of "economy" is a potential candidate; however, walking economy highly depends on speed, so direct comparisons of economy values are difficult between studies. We investigated whether the vertical component of net walking "efficiency" (Eff
; %) is constant across speed. In that case, direct comparisons of Eff
will be possible between studies or individuals at any voluntary speed.
Thirty young male participants walked at eight speeds on the level or ± 5% gradients, providing vertical speeds (v
). Differences in energy expenditure between level and uphill or downhill gradients (ΔEE) were calculated. The metabolic rate for vertical component (MR
) was calculated by multiplying ΔEE with body mass (BM). The mechanical power output for vertical component (P
) was calculated by multiplying BM, gravitational acceleration, and v
. Eff
was obtained from the ratio of P
to MR
at each v
. Delta efficiency (Delta-E; %) was also calculated from the inverse slope of the regression line representing the relationship of P
to MR
.
Upward Eff
was nearly constant at around 35% and downward Eff
ranged widely (49-80%). No significant differences were observed between upward Delta-E (35.5 ± 8.8%) and Eff
at any speeds, but not between downward Delta-E (44.9 ± 12.8%) and Eff
.
Upward ΔEE could be proportional to v
. Upward, but not downward, Eff
should be useful not only for healthy populations but also for clinical patients to evaluate individual gait characteristics, because it requires only two metabolic measurements on the level and uphill gradients without kinematic information at any voluntary speed.
UMIN000017690 (R000020501; registered May 26th, 2015, before the first trial) and UMIN000031456 (R000035911; registered Feb. 23rd, 2018, before the first trial).
Our present study investigated whether the ventilatory and gas exchange responses show different dynamics in response to sinusoidal change in cycle work rate or walking speed even if the metabolic ...demand was equivalent in both types of exercise. Locomotive parameters (stride length and step frequency), breath-by-breath ventilation (V̇E) and gas exchange (CO2 output (V̇CO2) and O2 uptake (V̇O2)) responses were measured in 10 healthy young participants. The speed of the treadmill was sinusoidally changed between 3 km·h-1 and 6 km·h-1 with various periods (from 10 to 1 min). The amplitude of locomotive parameters against sinusoidal variation showed a constant gain with a small phase shift, being independent of the oscillation periods. In marked contrast, when the periods of the speed oscillations were shortened, the amplitude of V̇E decreased sharply whereas the phase shift of V̇E increased. In comparing walking and cycling at the equivalent metabolic demand, the amplitude of V̇E during sinusoidal walking (SW) was significantly greater than that during sinusoidal cycling (SC), and the phase shift became smaller. The steeper slope of linear regression for the V̇E amplitude ratio to V̇CO2 amplitude ratio was observed during SW than SC. These findings suggested that the greater amplitude and smaller phase shift of ventilatory dynamics were not equivalent between SW and SC even if the metabolic demand was equivalent between both exercises. Such phenomenon would be derived from central command in proportion to locomotor muscle recruitment (feedforward) and muscle afferent feedback.
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