Hirokazu Genno

Effects of High-Intensity Interval Walking Training on Physical Fitness and Blood Pressure in Middle-Aged and Older People

OBJECTIVE To examine whether high-intensity interval walking training increased thigh muscle strength and peak aerobic capacity and reduced blood pressure more than moderate-intensity continuous walking training. PARTICIPANTS AND METHODS From May 18, 2004, to October 15, 2004 (5-month study period), 60 men and 186 women with a mean +/- SD age of 63 +/- 6 years were randomly divided into 3 groups: no walking training, moderate-intensity continuous walking training, and high-intensity interval walking training. Participants in the moderate-intensity continuous walking training group were instructed to walk at approximately 50% of their peak aerobic capacity for walking, using a pedometer to verify that they took 8000 steps or more per day for 4 or more days per week. Those in the high-intensity interval walking training group, who were monitored by accelerometry, were instructed to repeat 5 or more sets of 3-minute low-intensity walking at 40% of peak aerobic capacity for walking followed by a 3-minute high-intensity walking above 70% of peak aerobic capacity for walking per day for 4 or more days per week. Isometric knee extension and flexion forces, peak aerobic capacity for cycling, and peak aerobic capacity for walking were all measured both before and after training. RESULTS The targets were met by 9 of 25 men and 37 of 59 women in the no walking training group, by 8 of 16 men and 43 of 59 women in the moderate-intensity continuous walking training group, and by 11 of 19 men and 31 of 68 women in the high-intensity interval walking training group. In the high-intensity interval walking training group, isometric knee extension increased by 13%, isometric knee flexion by 17%, peak aerobic capacity for cycling by 8%, and peak aerobic capacity for walking by 9% (all, P<.001), all of which were significantly greater than the increases observed in the moderate-intensity continuous walking training group (all, P<.01). Moreover, the reduction in resting systolic blood pressure was higher for the high-intensity interval walking training group (P=.01). CONCLUSION High-intensity interval walking may protect against age-associated increases in blood pressure and decreases in thigh muscle strength and peak aerobic capacity.

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.

Effects of macronutrient intake on thigh muscle mass during home‐based walking training in middle‐aged and older women

We examined whether post‐exercise macronutrient supplementation during a 5‐month home‐based interval walking training (IWT) accelerated exercise‐induced increases in skeletal muscle mass and strength in healthy middle‐aged and older women. Thirty‐five women (41–78 years) were randomly divided into two groups: IWT alone (CNT, n = 18) or IWT plus post‐exercise macronutrient (7.6 g protein, 32.5 g carbohydrate, and 4.4 g fat) supplementation (NUT, n = 17). For IWT, all subjects were instructed to repeat five or more sets of 3‐min low‐intensity walking at 40% peak aerobic capacity (Vo2 peak), followed by a 3‐min high‐intensity walking above 70% Vo2 peak per day for 4 or more days per week. We determined Vo2 peak, thigh muscle tissue area by computer tomography, and thigh muscle strength in all subjects before and after IWT. We found that an increase in hamstring muscle tissue area was 2.8 ± 1.2% in NUT vs −1.0 ± 0.7% in CNT and that in isometric knee flexion force was 16.3 ± 3.7% in NUT vs 6.5 ± 3.0% in CNT; both were significantly higher in NUT than in CNT (both, P < 0.001). Thus, post‐exercise macronutrient supplementation enhanced the increases in thigh muscle mass and strength, although partially, in home‐based IWT in middle‐aged and older women.

Effects of mild calorie restriction and high-intensity interval walking in middle-aged and older overweight Japanese

We investigated whether a combination of mild calorie restriction (MCR) and high-intensity interval walking (HIW) improved physical fitness more than HIW alone in middle-aged and older overweight Japanese (40-69years old, BMI23.6kg/m(2)). Forty-seven women and 16 men were divided into MCR+HIW and HIW groups. All subjects performed HIW: 5 sets of 3-min low-intensity walking (40% peak aerobic capacity for walking, VO(2peak)) and 3-min high-intensity walking (70% VO(2peak)) per day, 4days per week, for 16weeks while energy expenditure was monitored with a tri-axial accelerometer. The MCR+HIW group consumed meal replacement formula (240kcal): a mixture of low-carbohydrates and -fat and high-protein, for either lunch or dinner everyday and therefore, had approximately 87% of the energy intake of the HIW group during the intervention period. Although the HIW group showed improvements in BMI, blood pressure, and several blood chemicals, the MCR+HIW group had greater improvement. Moreover, the medical expenditure for the 6months including the intervention period was 59% lower in the MCR+HIW group than in the HIW group. Our strategy of a short-term combination of MCR and HIW may thus prevent lifestyle-associated diseases and improve health in middle-aged and older overweight Japanese.

Attempt to control an artificial heart system using sympathetic nervous signals

Changes in skin sympathetic nerve activity (SSNA), which accelerates the constriction of peripheral blood vessels, were measured microneurographically from the median nerve of a subject, and were used for controlling the driving parameters of a pneumatically-driven artificial heart (AH) system. The number of SSNA pulses per second was calculated using a pulse counter, and the driving parameters (pulse rate, positive pressure, and vacuum pressure) of the artificial heart system were altered in accordance with the algorithm for changes in the number of SSNA pulses by means of batch processing. After that, the driving parameters and the pump output of the AH system and the arterial pressure of the mock circulatory system which was connected with the AH pump were compared with the SSNA, digital arterial pressure, and skin blood flow of the subject. The increase/decrease in the number of SSNA pulses essentially matched the changes in digital blood pressure and skin blood flow; in such cases, it was possible to alter the AH pump output and the arterial pressure of the mock circulatory system similar to the change in the actual hemodynamic data of the subject. The authors are currently planning to utilize cardiac nerve activity instead of SSNA.

Use of skin sympathetic nerve activity for the automatic control of an air-conditioning system

As the first stage of a long-term project aimed at developing an automatic control system for external devices which utilizes signals from the nervous system, the current study utilized changes in the skin sympathetic nervous activity (SSNA) measured microneurographically in order to accomplish the switching control of an external device between the cooling and heating modes. The number of SSNA (vasomotor) bursts decreased in proportion to the increase in the thermal sensation of the subject, demonstrating the possibility of operating an air-conditioner by using feedback from the number of SSNA bursts.

Evaluation of the physical activity of anesthesiologists in the operating room during daily work using a triaxial accelerometer.

Appropriate daily exercise is recommended to remain healthy for adults, including medical professionals. In this study, the authors quantified daily physical activity of anesthesiologists in the operating room using a newly developed triaxial accelerometer, Jukudai Mate. During daily work, mean ± SD energy expenditure of staff was 576 ± 181 kcal and was significantly higher than that of residents (400 ± 95 kcal; p =.007). The mean intensities of hourly physical activity of the staff and residents were estimated to be approximately 1.9 and 1.7 metabolic equivalents (METs), respectively. None of the anesthesiologists had more than 3 METs in intensity of physical activity. We concluded that the physical activity of anesthesiologists during daily work can be classified as light intensity. To promote and maintain health, anesthesiologists need physical activity of moderate or vigorous intensity off the job.

Analysis of sympathetic activity induced by stimulation

Brain waves, sympathetic nerve activity, blood flow, perspiration and skin temperature induced by sensation stimulation were simultaneously measured in order to analyze mechanisms that cause skin temperature changes associated with sensations. The results suggested that stimulation of the sympathetic nerve system, including skin temperature, is induced when intense stressful stimulation is recognized, and also indicated that the reaction gradually declines even though it may at times recover to the level of an initial reaction. The results also suggested that skin sympathetic nerve activity (in the case of vasomotor) may decline as ambient temperature rises.