Yoshiyuki Fukuoka

Methodological validation of the dynamic heterogeneity of muscle deoxygenation within the quadriceps during cycle exercise

The conventional continuous wave near-infrared spectroscopy (CW-NIRS) has enabled identification of regional differences in muscle deoxygenation following onset of exercise. However, assumptions of constant optical factors (e.g., path length) used to convert the relative changes in CW-NIRS signal intensity to values of relative concentration, bring the validity of such measurements into question. Furthermore, to justify comparisons among sites and subjects, it is essential to correct the amplitude of deoxygenated hemoglobin plus myoglobin [deoxy(Hb+Mb)] for the adipose tissue thickness (ATT). We used two time-resolved NIRS systems to measure the distribution of the optical factors directly, thereby enabling the determination of the absolute concentrations of deoxy(Hb+Mb) simultaneously at the distal and proximal sites within the vastus lateralis (VL) and the rectus femoris muscles. Eight subjects performed cycle exercise transitions from unloaded to heavy work rates (>gas exchange threshold). Following exercise onset, the ATT-corrected amplitudes (A(p)), time delay (TD(p)), and time constant (τ(p)) of the primary component kinetics in muscle deoxy(Hb + Mb) were spatially heterogeneous (intersite coefficient of variation range for the subjects: 10-50 for A(p), 16-58 for TD(p), 14-108% for τ(p)). The absolute and relative amplitudes of the deoxy(Hb+Mb) responses were highly dependent on ATT, both within subjects and between measurement sites. The present results suggest that regional heterogeneity in the magnitude and temporal profile of muscle deoxygenation is a consequence of differential matching of O(2) delivery and O(2) utilization, not an artifact caused by changes in optical properties of the tissue during exercise or variability in the overlying adipose tissue.

Kinetics of oxygen uptake and cardiac output at onset of arm exercise

Pulmonary oxygen uptake (V O2) kinetics at onset of exercise is reported to be slower for arm than for leg exercise. This could be attributed to reduced cardiac output (Q) or reduced arteriovenous O2 content difference or both. To test this, V O2 mean tissue oxygen consumption (V O2T) and Q kinetics in arm cranking were compared with corresponding values found in leg cycling. The increase in V O2 during phase 1 (abrupt increase after onset of exercise) was less in arm than in leg exercise, suggesting that immediate Q adjustments to arm exercise were less pronounced. Mean response times (MRT, the relative rates at which a steady state was attained) for V O2, V O2T, and Q were prolonged during arm exercise. The MRT of VO 2 in arm exercise at a given blood lactate increase was higher than in leg exercise. The delayed V O2 kinetics in arm exercise might be due to delayed Q kinetics and higher anaerobic glycolysis occurring early during arm exercise.

Finger Tapping Ability in Healthy Elderly and Young Adults

PURPOSE The maximum isometric force production capacity of the fingers decreases with age. However, little information is available on age-related changes in dynamic motor capacity of individual fingers. The purpose of this study was to compare the dynamic motor function of individual fingers between elderly and young adults using rapid single-finger and double-finger tapping. METHODS Fourteen elderly and 14 young adults performed maximum frequency tapping by the index, middle, ring, or little finger (single-finger tapping) and with alternate movements of the index-middle, middle-ring, or ring-little finger-pair (double-finger tapping). The maximum pinch force between the thumb and each finger, tactile sensitivity of each fingertip, and time taken to complete a pegboard test were also measured. RESULTS Compared with young subjects, the older subjects had significantly slower tapping rates in all fingers and finger-pairs in the tapping tasks. The age-related decline was also observed in the tactile sensitivities of all fingers and in the pegboard test. However, there was no group difference in the pinch force of any finger. The tapping rate of each finger did not correlate with the pinch force or tactile sensitivity for the corresponding finger in the elderly subjects. CONCLUSIONS Maximum rate of finger tapping was lower in the elderly adults compared with the young adults. The decline of finger tapping ability in elderly adults seems to be less affected by their maximum force production capacities of the fingers as well as tactile sensitivities at the tips of the fingers.

System Analysis for Oxygen Uptake Kinetics with Step and Pseudorandom Binary Sequence Exercise in Endurance Athletes

We examined whether the system analysis for step and pseudorandom binary sequence (PRBS) exercises could be useful to characterize oxygen uptake (VO2) kinetics of female sedentary subjects and endurance athletes. Breath-by-breath VO2 was determined during step- and PRBS-cycle ergometer exercises. The time course of the VO2 kinetics was evaluated by the time constant of the second phase, which should reflect the adjustment of the oxidative metabolism at the skeletal muscle level. The VO2 kinetics were significantly faster in long-distance runners than in sedentary subjects for both exercises. A significant relationship was observed in the VO2 kinetics obtained from step and PRBS exercises. In each group, there was no significant difference in the VO2 kinetics for step and PRBS exercises. These results indicated that the system analysis with PRBS exercises revealed the faster VO2 kinetics in endurance athletes than in sedentary subjects.

Kinetics and steady-state of VO2 responses to arm exercise in trained spinal cord injury humans.

Study design: Cross-sectional study comparing trained spinal cord injured (SCI) subjects (lesion level: L1∼T6) with healthy young subjects (CONT).Objective: To investigate the kinetics of response in oxygen uptake ([Vdot ]O2) in human upper-body skeletal muscles, nine trained SCI subjects underwent submaximal supine arm exercises.Method: The SCI subjects underwent an incremental arm exercise test until exhaustion. The days after this first round of testing, breath-by-breath [Vdot ]O2 and beat-by-beat heart rate (HR) on- and off-kinetics were determined during three repetitions of constant exercise at 50% of [Vdot ]O2peak. The overall time course of response was determined from the half time (t1/2). Increased capillary blood lactate production (Δ[La]b) at the onset of exercise was defined as the difference between at rest and at the end of exercise. Cardiac output ([Qdot ]) was measured using the acetylene rebreathing method during the steady state of exercise. In accordance with the Fick principle, the difference in arterial-venous O2 content (Ca-vO2) was defined as [Vdot ]O2/[Qdot ].Results: During the steady state of the submaximal arm exercise, a more significant increase in the steady state of [Qdot ] was obtained in the CONT subjects than in the trained SCI subjects: respectively, 14.9±1.4 l/min versus (12.7±0.8 l/min). There was no difference in the steady state of [Vdot ]O2 between the two groups; as a result, SCI subjects had the greater Ca-v2. Meanwhile,[Vdot ]O2 on- and off-kinetics became much faster in the trained SCI subjects than in the CONT subjects. In addition, t1/2 HR on-kinetics was not significantly different between the SCI and CONT groups. Increased Δ[La]b was closely related to larger t1/2 [Vdot ]O2 on-kinetics (r=0.624, P<0.05).Conclusion: It is concluded that the acceleration of [Vdot ]O2 on- and off-kinetics in the trained SCI subjects was observed even though there was no difference in HR on- and off-kinetics between the SCI and CONT groups and a lower steady state of [Qdot ] in the trained SCI subjects. [Vdot ]O2 kinetics would therefore be the limiting factor in oxidative phosphorylation in the upper skeletal muscles, thereby providing a lower lactic O2-deficit (ie Δ[La]b).Sponsorship: This study was partly supported by the grant from Frontier Science Promotion in Kumamoto, Japan (1997, 1998).

The effects of exercise intensity on thermoregulatory responses to exercise in women

We investigated the influence of altering exercise intensity (150, 300, and 450 kpm/min) on the resetting of the core temperature threshold for the onset of the sweating rate (M(sw)) and the alteration of sweating sensitivity during the menstrual cycle in women. Five women underwent cycling exercise for 30 min in both the luteal and follicular phases under controlled neutral environmental conditions (T: 25 degrees C, RH: 55%). A significantly higher rectal temperature (T(re)) was seen in the luteal phase at all exercise intensities, and the same time course of the T(re) response with a constant difference of approximately 0.2 degrees C was shown between the follicular phase and the luteal phase. The T(re) threshold for M(sw) was also apparently shifted rightward a constant value of 0.2 degrees C from the follicular phase to the luteal phase, independent of the alteration of exercise intensity. The slope of the M(sw)-T(re) relationship in the follicular phase did not differ from that in the luteal phase. These results indicate that (1) a rightward shift in the T(re) threshold from the follicular phase to the luteal phase can be observed independent of any alteration of the exercise intensity; and (2) the sensitivity of M(sw) is also not physiologically influenced by exercise intensity. Thus, alterative thermoregulation during the menstrual cycle was fundamentally unaffected by the change of exercise intensity.

Effects of wheelchair training on [Vdot]O2 kinetics in the participants with spinal-cord injury

Purpose. We tested the hypothesis that, in eight participants (seven males, one female; 46.5 ± 8.3 years) with spinal-cord injury (complete lesions, T7-L1), the effects of exercise training on pulmonary O2 uptake ([Vdot]O2) on- and off- kinetics would appear early in this pilot study. Methods. The subjects underwent the wheelchair-training program (3 day/w, 30 min/day, and 50% HRreserve), and were evaluated before training (“time 0”, T0), and after 7 (T7), 15 (T15), 30 (T30), and 60 (T60) days of training. Breath-by-breath peak [Vdot]O2 was determined during the incremental exercise until their exhaustion. At another day following the incremental exercise, the subjects performed three repetitions of a constant exercise at 50% peak [Vdot]O2 workload so that [Vdot]O2 could be determined for both on- and off-kinetics. Results and conclusion. Peak [Vdot]O2 showed a tendency to increase with training; the increases became significant at T30. The time constants (τ2) during “phase II” of the [Vdot]O2 on-kinetics were 62.4 ± 13.0 (s) (T0), 51.2 ± 8.7 (T7), 46.1 ± 7.4 (T15), 45.0 ± 7.2 (T30), and 43.4 ± 6.4 (T60); a significant difference compared to T0 was observed from T7 onward. The same pattern of change as a function of training was described for the [Vdot]O2 off-kinetics. It is concluded that in SCI participants, the acceleration of [Vdot]O2 kinetics at the onset of exercise was observed over a short term.

Economical Speed and Energetically Optimal Transition Speed Evaluated by Gross and Net Oxygen Cost of Transport at Different Gradients

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.

Respiratory variability in R-R interval during sinusoidal exercise.

Abstract The R-R interval varies with the cycles of respiration. The response of the variability in the R-R interval with respiration was examined during sinusoidal cycle exercise in 12 healthy young male subjects. Work rate varied sinusoidally between 30 W and 60% maximal oxygen uptake for an 8-min period. The higher the heart rate (HR), the smaller was the magnitude of the variation in R-R interval with respiration (ΔRR). When HR increased with an increase in exercise intensity, however, ΔRR tended to decrease more markedly at lower HR. On the other hand, since ΔRR generally increased linearly during the decrease in HR with a reduction in exercise intensity, ΔRR was greater during decreases in HR than during increases in HR at a similar HR. These results suggest that the contribution of the withdrawal of cardiac parasympathetic activity to increases in HR with increases in exercise intensity during sinusoidal exercise were greater at lower HR, and that the cardiac parasympathetic system was more activated during HR decreases than during HR increases at the same HR. From our findings it would seem that such complex parasympathetic HR regulaltion during sinusoidal exercise, which depends on the level of HR and the direction of the change in HR, may be influenced by factors other than the parasympathetic system, such as the cardiac sympathetic system.

Walking economy at simulated high altitude in human healthy young male lowlanders

ABSTRACT We measured oxygen consumption during walking per unit distance (Cw) values for 12 human healthy young males at six speeds from 0.667 to 1.639 m s−1 (four min per stage) on a level gradient under normobaric normoxia, moderate hypoxia (15% O2), and severe hypoxia (11% O2). Muscle deoxygenation (HHb) was measured at the vastus lateralis muscle using near-infrared spectroscopy. Economical speed which can minimize the Cw in each individual was calculated from a U-shaped relationship. We found a significantly slower economical speed (ES) under severe hypoxia [1.237 (0.056) m s−1; mean (s.d.)] compared to normoxia [1.334 (0.070) m s−1] and moderate hypoxia [1.314 (0.070) m s−1, P<0.05 respectively] with no differences between normoxia and moderate hypoxia (P>0.05). HHb gradually increased with increasing speed under severe hypoxia, while it did not increase under normoxia and moderate hypoxia. Changes in HHb between standing baseline and the final minute at faster gait speeds were significantly related to individual ES (r=0.393 at 1.250 m s−1, r=0.376 at 1.444 m s−1, and r=0.409 at 1.639 m s−1, P<0.05, respectively). These results suggested that acute severe hypoxia slowed ES by ∼8%, but moderate hypoxia left ES unchanged. Summary: Acute severe hypoxia slowed the economical speed (ES) which can minimize energy cost of walking. Muscle O2 extraction may be one of the determining factors of an individuals ES.