Effect of arm cranking on the NIRS-determined blood volume and oxygenation of human inactive and exercising vastus lateralis muscle

In this study, the effects of arm cranking on total (HbT) and oxygenated haemoglobin concentrations (HbO₂) of inactive and exercising vastus lateralis muscles were investigated using near-infrared spectrometry (NIRS). Four exercise protocols were performed, 6-min arm cranking at intensities of 30% and 50% of peak oxygen uptake ( , recorded during incremental arm exercise; AE₃₀ and AE₅₀, respectively), and 6 min of combined exercise in which AE₃₀ or AE₅₀ was added to on-going leg cycling at an intensity of 40% (LE₄₀: AE₃₀LE₄₀ and AE₅₀LE₄₀, respectively). During AE₃₀ in the inactive vastus lateralis, neither HbT nor HbO₂ changed from the control values, whereas they both decreased during AE₅₀. The decrease in HbT was observed from the 1st to the 5th min of exercise, whereas the decrease in HbO₂ was observed from the 3rd to the 6th min of exercise. In the exercising vastus lateralis, neither HbT nor HbO₂ changed from the control value during AE₃₀LE₄₀. In addition, HbO₂ did not change during AE₅₀LE₄₀. During AE₅₀LE₄₀, however, although HbT did not change from the 1st to the 4th min of exercise, it increased from the 4th to the 6th min. These results indicate that although in the inactive vastus lateralis both HbT and HbO₂ decrease during moderate arm exercise, these decreases are suppressed in the exercising vastus lateralis muscle. Electronic Publication     

Oxygen uptake and heart rate kinetics during heavy exercise: a comparison between arm cranking and leg cycling

This study examined the oxygen uptake (V˙O₂) and heart rate (HR) kinetics during arm cranking and leg cycling at work rates above the anaerobic threshold (AT). Ten untrained male subjects [21.6 (1.3) years] completed two 7 min 15 s constant-load arm cranking and two leg cycling tests at a power output halfway between the mode-specific AT and peak V˙O₂. The time constants for phase II V˙O₂ (τ) and HR (τ) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. V˙O₂ τ and HR τ values were significantly (P<0.001) slower in arm cranking [V˙O₂ τ = 66.4 (3.0) s; HR τ = 74.7 (4.4) s] than in leg cycling [V˙O₂ τ = 42.0 (1.9) s; HR τ = 55.6 (3.5) s]. The V˙O₂ slow component (V˙O_2SC) accounted for a significantly (P<0.001) greater percentage of the total exercise response during arm cranking [23.8 (1.6)%] than during leg cycling [14.2 (1.5)%]. The greater relative V˙O_2SC and the slower V˙O₂ τ with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling. Electronic Publication     

Ventilatory responses at the onset of passive movement and voluntary exercise with arms and legs

This study was undertaken to elucidate whether phase I appeared at the onset of voluntary and passive arm movements and to compare these results with those of similar leg movements. Instead of the conventional cranking exercise, seven male subjects performed alternately flexion-relaxation of both arms, extension-relaxation of both legs, and combined arm and leg exercise at the rate of about 60 min^-1 for four breaths in a sitting position. Similar movements were accomplished passively by the experimenters. In all experiments, minute ventilation increased rapidly within the first breath after the onset of exercise. The difference of ventilation (delta value) between the mean of the first two breaths at the onset of voluntary exercise and that of five breaths during rest was significantly (P < 0.05) greater in arm (7.751 min^-1) than in leg (5.191 min^-1). Passive movement showed a similar tendency. Arm delta ventilation correlated highly (r = 0.74 ± 0.91) with leg delta ventilation and the slope of the regression lines was about 1.2. Heart rate increased abruptly while cardiac output did not always increase rapidly at the onset of locomotion. Oxygen uptake in the voluntary leg exercise continued for 3 min was slightly but nonsignificantly higher than in the arm exercise, indicating the equality of the exercise intensity. In conclusion, ventilatory responses at the onset of the arm exercise are larger than those of the leg in both voluntary and passive conditions regardless of the muscle mass, suggesting the different neurogenic mechanism between arm and leg.     

Muscle phosphocreatine and pulmonary oxygen uptake kinetics in children at the onset and offset of moderate intensity exercise

To further understand the mechanism(s) explaining the faster pulmonary oxygen uptake kinetics found in children compared to adults, this study examined whether the phase II kinetics in children are mechanistically linked to the dynamics of intramuscular PCr, which is known to play a principal role in controlling mitochondrial oxidative phosphorylation during metabolic transitions. On separate days, 18 children completed repeated bouts of moderate intensity constant work-rate exercise for determination of (1) PCr changes every 6 s during prone quadriceps exercise using ³¹P-magnetic resonance spectroscopy, and (2) breath by breath changes in during upright cycle ergometry. Only subjects (n = 12) with 95% confidence intervals ≤±7 s for all estimated time constants were considered for analysis. No differences were found between the PCr and phase II time constants at the onset (PCr 23 ± 5 vs. or offset (PCr 28 ± 5 vs. of exercise. The average difference between the PCr and phase II time constants was 4 ± 4 s for the onset and offset responses. Pooling of the exercise onset and offset responses revealed a significant correlation between the PCr and time constants (r = 0.459, P = 0.024). The close kinetic coupling between the and PCr responses at the onset and offset of exercise in children is consistent with our current understanding of metabolic control and suggests that an age-related modulation of the putative phosphate linked controller(s) of mitochondrial oxidative phosphorylation may explain the faster kinetics found in children compared to adults.     

Recovery dynamics of skeletal muscle oxygen uptake during the exercise off-transient

The time course of muscle recovery from contractions (i.e., muscle off-kinetics), measured directly at the site of O₂ exchange, i.e., in the microcirculation, is unknown. Whereas biochemical models based upon creatine kinase flux rates predict slower off- than on-transients [Kushmerick, M.J., 1998. Comp. Biochem. Physiol. B: Biochem. Mol. Biol.] whole muscle data [Krustrup, et al. J. Physiol.] suggest on–off symmetry.

Purpose

We tested the hypothesis that the slowed recovery blood flow (Qm) kinetics profile in the spinotrapezius muscle [Ferreira et al., 2006. J. Physiol.] was associated with a slowed muscle recovery compared with that seen at the onset of contractions (time constant, τ  23 s, Behnke et al., 2002. Resp. Physiol.), i.e., on–off asymmetry.

Methods

Measurements of capillary red blood cell flux and microvascular pressure of O₂ (P_O2mv) were combined to resolve the temporal profile of muscle across the moderate intensity contractions-to-rest transition.

Results

Muscle decreased from an end-contracting value of 7.7 ± 0.2 ml/100 g/min to 1.7 ± 0.1 ml/100 g/min at the end of the 3 min recovery period, which was not different from pre-stimulation . Contrary to our hypothesis, muscle in recovery began to decrease immediately (i.e., time delay <2 s) and demonstrated rapid first-order kinetics (τ, 25.5 ± 2.6 s) not different (i.e., symmetrical to) to those during the on-transient. This resulted in a systematic increase in microvascular P_O2 during the recovery from contractions.

Conclusions

The slowed Qm kinetics in recovery serves to elevate the ratio and thus microvascular P_O2. Whether this Qm response is obligatory to the rapid muscle kinetics and hence speeds the repletion of high-energy phosphates by maximizing conductive and diffusive O₂ flux is an important question that awaits resolution.     

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

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). 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 online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.