Yoshi-ichiro Kamijo

A New Device to Estimate V˙O2 during Incline Walking by Accelerometry and Barometry

PURPOSE To examine whether the biased estimation of oxygen consumption rate (VO2, mL x kg(-1) x min(-1)) by accelerometry during incline walking can be improved by the addition of altitude changes as measured by barometry. METHODS We measured VO2 by respiratory gas analysis and vector magnitude (VM, G) from triaxial accelerations in 42 healthy people (mean +/- SD age = 63 +/- 7 yr) during graded walking on a treadmill while the incline was varied from -15% to +15%. They walked at subjectively slow, moderate, and fast speeds on level and uphill inclines and, in addition to these, at their fastest speed at 0% incline. They then walked at approximately 3, 4, and 5 km x h(-1) on downhill inclines for 3 min each. We determined a regression equation to estimate VO2 from VM and theoretical vertical upward (Hu, m x min(-1)) and downward speeds (Hd, m x min(-1)) for the last 1 min of each trial. To validate the precision of the equation, we measured VM and altitude changes with a portable device equipped with a triaxial accelerometer and a barometer in 11 of the 42 subjects walking on an outdoor hill and compared the estimated VO2 with the value simultaneously measured by respiratory gas analysis. RESULTS VO2 above resting was estimated from VO2 = 0.044 VM + 1.365 Hu + 0.553 Hd (r = 0.93, P < 0.001) and the estimated V O2(y) was almost identical to the measured VO2(x) (y = 0.97x, r = 0.88, P < 0.001) with a mean difference of -0.20 +/- 3.47 (mean +/- SD) by Bland-Altman analysis in the range of 2.0-33.0 mL x kg(-1) x min(-1). CONCLUSIONS VO2 during walking on various inclines can be precisely estimated by using the device equipped with a triaxial accelerometer and a barometer.

Physical fitness and indices of lifestyle-related diseases before and after interval walking training in middle-aged and older males and females

Hypothesis Whether increasing peak aerobic capacity for walking (V̇2peak) by interval walking training (IWT) is closely linked with decreasing the indices of lifestyle-related diseases (LSDs) in middle-aged and older people were examined. Methods For 4 months from April to September 2005 or 2006, 246 males and 580 females (∼65 years) performed IWT consisting of ≥5 sets of fast walking at ≥70% V̇2peak for 3 min followed by slow walking at ≤40% V̇2peak for 3 min ≥4 days/week. Before and after IWT, we measured V̇2peak, body mass index (BMI), %body fat, arterial blood pressure, thigh muscle strength and blood parameters. We analysed 198 males and 468 females who had undergone all the measurements both before and after IWT. To examine the hypothesis, we divided the subjects equally into three groups according to their pretraining V̇2peak: low, middle and high groups for each sex. Results Before training, it was found that thigh muscle strength and blood high-density lipoprotein cholesterol concentration were lower, whereas body weight, BMI, %body fat, arterial blood pressure and blood glucose were higher in the low group than the high group (all, p<0.05). After training, although V̇2peak and thigh muscle strength increased and body weight, BMI, %body fat, blood pressure and blood glucose concentration decreased in all groups (all, p<0.05), the changes were greatest in the low group for both sexes. Conclusion V̇2peak at baseline and changes in response to training were closely linked with indices of LSDs.

Beyond epidemiology: field studies and the physiology laboratory as the whole world

There is no exercise training regimen broadly available in the field to increase physical fitness and prevent lifestyle‐related diseases in middle‐aged and older people. We have developed interval walking training (IWT) repeating five or more sets of 3 min fast walking at ≥70% peak aerobic capacity for walking (w) per day with intervening 3 min slow walking at 40% w, for ≥4 days week−1, for ≥5 months. Moreover, to determine w in individuals and also to measure their energy expenditure even while incline walking, we have developed a portable calorimeter. Further, to instruct subjects on IWT even if they live remotely from the trainers, we have developed e‐Health Promotion System. This transfers individual energy expenditure during IWT stored on the meter to a central server through the internet; it sends back the achievement to individuals along with advice generated automatically by the sever according to a database on ≥4000 subjects. Where we found that 5 months of IWT increased physical fitness and improved the indices of lifestyle‐related diseases by 10–20% on average. Since our system is run at low cost with fewer staff for more subjects, it enables us to develop exercise prescriptions appropriate for individuals.

Triaxial accelerometry to evaluate walking efficiency in older subjects.

PURPOSE We tested the suitability of triaxial accelerometry to evaluate walking efficiency in older subjects. METHODS First, we verified the accuracy to estimate the oxygen consumption rate (.VO2, mL.min-1) from the total impulse (Itotal, N.min-1), the square root of summed accelerations of each direction, during graded walking on a flat ground in 13 male and 27 female older subjects (61 +/- 6 yr, mean +/- SD). Second, to examine the effects of endurance/resistance training on walking efficiency, we assessed the relations of maximal isometric knee extension force (Fmax, N.m), maximal walking velocity (Vmax, m.min-1), and three-dimensional impulses (Ix, anterior-posterior; Iy, mediolateral; Iz, vertical) in 13 male and 40 female older subjects (62 +/- 7 yr) before and after 6 and 9 months of training. RESULTS The following analyses were performed in all the data from the male and female groups. First, .VO2 was highly correlated with Itotal (r = 0.958, P < 0.0001) over the range of 250-2200 mL.min-1. Second, Fmax and Vmax increased by 48 +/- 7% (P < 0.001) and 21 +/- 2% (P < 0.001), respectively, after 9 months of training. Ix/Itotal and Iy/Itotal increased by 18 +/- 2% (P < 0.001) and 10 +/- 2%, respectively, after 9 months of training (P < 0.001), whereas Iz/Itotal decreased by 14 +/- 2% (P < 0.001). Vmax was negatively correlated with Iz/Itotal (r = -0.522, P < 0.0001) while positively correlated with Ix/Itotal (r = 0.561, P < 0.0001) and Iy/Itotal in the pooled data from before, after 6 and 9 months of training. Similarly, the product of Vmax and body weight was positively correlated with Fmax (r = 0.633, P < 0.0001). CONCLUSIONS These results suggest that increased Fmax improved walking efficiency by increasing energy utilization in the anterior-posterior/mediolateral directions while decreasing energy loss in the vertical direction.

Effects of hypohydration on thermoregulation during exercise before and after 5-day aerobic training in a warm environment in young men

We examined whether enhanced cardiovascular and thermoregulatory responses during exercise after short-term aerobic training in a warm environment were reversed when plasma volume (PV) expansion was reversed by acute isotonic hypohydration. Seven young men performed aerobic training at the 70% peak oxygen consumption rate (Vo(₂peak)) at 30°C atmospheric temperature and 50% relative humidity, 30 min/day for 5 days. Before and after training, we performed the thermoregulatory response test while measuring esophageal temperature (T(es)), forearm skin vascular conductance, sweat rate (SR), and PV during 30 min exercise at the metabolic rate equivalent to pretraining 65% Vo(₂peak) in euhydration under the same environment as during training in four trials (euhydration and hypohydration, respectively). Hypohydration targeting 3% body mass was attained by combined treatment with low-salt meals to subjects from ~48 h before the test and administration of a diuretic ~4 h before the test. After training, the T(es) thresholds for cutaneous vasodilation and sweating decreased by 0.3 and 0.2°C (P = 0.008 and 0.012, respectively) when PV increased by ~10%. When PV before and after training was reduced to a similar level, ~10% reduction from that in euhydration before training, the training-induced reduction in the threshold for cutaneous vasodilation increased to a level similar to hypohydration before training (P = 0.093) while that for sweating remained significantly lower than that before training (P = 0.004). Thus the enhanced cutaneous vasodilation response after aerobic training in a warm environment was reversed when PV expansion was reversed while the enhanced SR response remained partially.

Protein and carbohydrate supplementation during 5-day aerobic training enhanced plasma volume expansion and thermoregulatory adaptation in young men

We examined whether protein and carbohydrate (CHO) supplementation during 5-day training enhanced plasma volume (PV) expansion and thermoregulatory and cardiovascular adaptations in young men. Eighteen men [age 23 ± 4 (SD) yr] were divided into two groups according to supplements: placebo (CNT: 0.93 kcal/kg, 0.00 g protein/kg, n = 9) and protein and CHO (Pro-CHO: 3.6 kcal/kg, 0.36 protein/kg, n = 9). Subjects in both groups performed a cycling exercise at 70% peak oxygen consumption rate (VO2peak), 30 min/day, for 5 consecutive days at 30°C ambient temperature and 50% relative humidity and took either a placebo or Pro-CHO within 10 min after exercise for each day. Before and after training, PV at rest, heart rate (HR), and esophageal temperature (T(es)) during 30-min exercise at 65% of pretraining VO2peak in the same condition as training were determined. Also, the sensitivity of the chest sweat rate (ΔSR/ΔT(es)) and forearm vascular conductance (ΔFVC/ΔT(es)) in response to increased T(es) were determined. After training, PV and cardiac stroke volume (SV) at rest increased in both groups (P < 0.001) but the increases were twofold higher in Pro-CHO than CNT (P = 0.007 and P = 0.078, respectively). The increases in HR from 5 to 30 min and T(es) from 0 to 30 min of exercise were attenuated after training in both groups with greater attenuation in Pro-CHO than CNT (P = 0.002 and P = 0.072, respectively). ΔSR/ΔT(es) increased in CNT (P = 0.052) and Pro-CHO (P < 0.001) and the increases were higher in Pro-CHO than CNT (P = 0.018). ΔFVC/ΔT(es) increased in Pro-CHO (P < 0.001), whereas not in CNT (P = 0.16). Thus protein-CHO supplementation during 5-day training enhanced PV expansion and thermoregulatory adaptation and, thereby, the reduction in heat and cardiovascular strain in young men.

Skin sympathetic nerve activity component synchronizing with cardiac cycle is involved in hypovolaemic suppression of cutaneous vasodilatation in hyperthermia

Non‐technical summary  Thermoregulatory responses during exercise are reduced following thermal dehydration. If individuals do not rehydrate adequately, it could lead to heat exhaustion or stroke with the worst case scenario being death. Plasma volume loss during dehydration has been suggested to suppress cutaneous vasodilatation in response to hyperthermia via a baroreflex‐mediated reduction in active vasodilator activity rather than enhanced active vasoconstrictor activity. However, no changes in the electrical signals of the efferent neural pathway have ever been identified. In the present study, we found a component of efferent skin sympathetic nerve activity that was synchronized with the cardiac cycle in thermally stressed individuals. This nerve activity increased with an increase in oesophageal temperature and the increase was significantly suppressed by hypovolaemia. Thus, this component of skin sympathetic nerve activity might represent the active vasodilator signals that regulate skin blood flow during hyperthermia in humans.

Transient cutaneous vasodilatation and hypotension after drinking in dehydrated and exercising men.

We examined whether oropharyngeal stimulation by drinking released the dehydration‐induced suppression of cutaneous vasodilatation and decreased mean arterial pressure (MAP) in exercising subjects, and assessed the effects of hypovolaemia or hyperosmolality alone on these responses. Seven young males underwent four hydration conditions. These were two normal plasma volume (PV) trials: normal plasma osmolality (Posmol, control trial) and hyperosmolality (ΔPosmol=+11 mosmol (kg H2O)−1); and two low PV trials: isosmolality (ΔPV =−310 ml) and hyperosmolality (ΔPV =−345 ml; ΔPosmol=+9 mosmol (kg H2O)−1), attained by combined treatment with furosemide (frusemide), hypertonic saline and/or 24 h water restriction. In each trial, the subjects exercised at 60% peak aerobic power for ∼50 min at 30°C atmospheric temperature and 50% relative humidity. When oesophageal temperature (Toes) reached a plateau after ∼30 min of exercise, the subjects drank 200 ml water at 37.5°C within a minute. Before drinking, forearm vascular conductance (FVC), calculated as forearm blood flow divided by MAP, was lowered by 20–40% in hypovolaemia, hyperosmolality, or both, compared with that in the control trial, despite increased Toes. After drinking, FVC increased by ∼20% compared with that before drinking (P < 0.05) in both hyperosmotic trials, but it was greater in normovolaemia than in hypovolaemia (P < 0.05). However, no increases occurred in either isosmotic trial. MAP fell by 4–8 mmHg in both hyperosmotic trials (P < 0.05) after drinking, but more rapidly in normovolaemia than in hypovolaemia. PV and Posmol did not change during this period. Thus, oropharyngeal stimulation by drinking released the dehydration‐induced suppression of cutaneous vasodilatation and reduced MAP during exercise, and this was accelerated when PV was restored.

Reduced hyperthermia-induced cutaneous vasodilation and enhanced exercise-induced plasma water loss at simulated high altitude (3,200 m) in humans

We examined whether less convective heat loss during exercise at high altitude than at sea level was partially caused by reduced cutaneous vasodilation due to enhanced plasma water loss into contracting muscles and whether it was caused by hypoxia rather than by hypobaria. Seven young men performed cycling exercise for 40 min at 50% peak aerobic power in normoxia at (710 mmHg) 610 m, determined before the experiments, in three trials: 1) normobaric normoxia at 610 m (CNT), 2) hypobaric hypoxia [low pressure and low oxygen (LPLO)] at 3,200 m (510 mmHg), 3) normobaric hypoxia [normal pressure and low oxygen (NPLO)] at 610 m, in an artificial climate chamber where atmospheric temperature and relative humidity were maintained at 30°C and 50%, respectively. Subjects in CNT and LPLO breathed room air, whereas those in NPLO breathed a mixed gas of 14% O₂ balanced N₂, equivalent to the gas composition in LPLO. We measured change in PV (ΔPV), oxygen consumption rate (Vo₂), mean arterial blood pressure (MBP), esophageal temperature (T(es)), mean skin temperature (T(sk)), forearm skin blood flow (FBF), and sweat rate (SR) during exercise. Although Vo₂, MBP, T(sk), and SR responses during exercise were similar between trials (P > 0.05), the sensitivity of forearm vascular conductance (FBF/MBP) in response to increased T(es) was lower in LPLO and NPLO than in CNT (P < 0.05), whereas that of SR was not, resulting in a greater increase in T(es) from minute 5 to 40 of exercise in LPLO and NPLO than in CNT (P = 0.026 and P = 0.011, respectively). ΔPV during exercise was twofold greater in LPLO and NPLO than in CNT. These variables were not significantly different between LPLO and NPLO. Thus reduced convective heat loss during exercise at 3,200 m was partially caused by reduced cutaneous vasodilation due to enhanced PV loss. Moreover, this may be caused by hypoxia rather than by hypobaria.

Enhanced renal Na+ reabsorption by carbohydrate in beverages during restitution from thermal and exercise-induced dehydration in men

We examined whether carbohydrate in beverages accelerated fluid retention during recovery from thermal and exercise-induced dehydration and whether it was caused in part by an enhanced renal Na+ reabsorption rate due to insulin secretion. After dehydrating by ∼2.3% body weight by exercise in a hot environment, seven young men underwent high-carbohydrate, low-carbohydrate, or control rehydration trials by drinking one of three beverages with 3.4 g glucose + 3.1 g fructose, 1.7 g glucose + 1.6 g fructose, or 0.0 g glucose + 0.0 g fructose per deciliter, respectively, in a common composition of electrolyte solution: 21 meq/l [Na+], 5 meq/l [K+], 16.5 meq/l [Cl-], 10 meq/l [citrate(-3)]. They drank the same amount of beverage as total body weight loss within 30 min. During the 60 min before the start of drinking and the following 180 min, we measured plasma volume (PV), plasma glucose ([Glc]p), serum insulin ([Ins]s), plasma Na+ concentrations, and the renal clearances of inulin, lithium, and Na+ with plasma vasopressin ([AVP]p) and aldosterone concentrations ([Ald]p) every 30 min. After dehydration, PV decreased by ∼5% and plasma osmolality increased by ∼6 mosmol/kg H2O in all trials with no significant differences among them. We found in the high-carbohydrate trial that 1) PV increased faster than in the control trial and remained at the higher level than other trials for the last 60 min (P < 0.05); 2) accumulated urine volume was smallest after 90 min (P < 0.05); 3) the renal Na+ reabsorption rate was greatest for the first 120 min (P < 0.05); 4) during which period [AVP]p and [Ald](p) were not significantly different from other trials (both, P > 0.9); and 5) [Glc](p) and [Ins]s were highest from 45 to 105 min (P < 0.05) during rehydration. Thus carbohydrate in beverages enhances renal Na+ reabsorption, and insulin is possibly involved in this enhancement.