Influence of four weeks of n-3 polyunsaturated fatty acid supplementation on fat metabolism during prolonged exercise / 体力科学

Glycogen is an important source of energy production during endurance exercise, such as marathon. Due to limited storage of glycogen in muscle and liver, augmentation of fat oxidation is known to delay depletion of muscle glycogen, leading to improvement of endurance performance. N-3 polyunsaturated fatty acids (n-3 PUFA) resulting from the form of fish has shown to enhance fat oxidation at rest. However, effect of n-3 PUFA on substrate metabolism during prolonged exercise remains unclear. The present study was designed to investigate whether dietary n-3 PUFA enhances fat oxidation during exercise and endurance performance. Thirteen healthy men were divided into n-3 PUFA group [n=6, 6g/day of fish oil; 1,800mg eicosapentaenoic acid (EPA), 2,700mg docosahexiaenoic acid (DHA)] or CON group [n=7, 6g/day of olive oil]. The subjects ingested each supplement for 4-weeks. Before and after the treatment period, a 60-min pedaling exercise at 65% of maximal oxygen uptake followed by 5 km-time-trial was conducted. Resting concentrations of serum EPA and DHA, EPA/AA were significantly elevated in the n-3 PUFA group only. After supplementation period, the n-3 PUFA group increased significantly exercise-induced elevations of serum free fatty acids and glycerol concentrations, and lowered respiratory exchange ratio during a 60-min pedaling exercise. Similar changes were not observed in the CON group. However, treatment with n-3 PUFA did not affect significantly result of 5km-time-trial. Four-week supplementation of n-3 PUFA increased exercise-induced lipolysis and fat oxidation during prolonged exercise. However, the augmented fat metabolism did not affect endurance performance.

PHYSICAL ACTIVITY PATTERNS AND PHYSICAL FITNESS LEVELS OF HOMEBOUND ELDERLY PEOPLE LIVING IN THE COMMUNITY / 体力科学

There have so far been no studies examining the physical fitness and physical activity (PA), measured using objective measures, in homebound elderly people. The purpose of this study was to examine physical fitness levels and PA patterns and evaluate their relationships in homebound elderly people. In 2004, a total of 3964 community-dwelling elderly aged 65 years and over participated in a base line survey. The subject data were directly collected by in-home interviewer. Subjects were defined as being homebound if they went outdoors less than once a week. However, the subjects who could not go out without assistance due to sickness and/or disability were excluded from the analysis. In 2005, 38 homebound (22 men, 16 women) and 70 non-homebound (33 men, 37 women) older adults who participated in the base line survey were selected. Measurements of physical fitness levels and PA patterns measured using an accelerometer, were taken in 2005. The total steps per day did not significantly differ between homebound and non-homebound men and women. The time spent in 1.8 METs activity (corresponding to activity level 1 of the accelerometer) was significantly higher in women than in men for non-homebound and homebound, respectively. The time spent in lower-, moderate-, and high-intensity PA did not significantly differ between homebound and non-homebound men and women, respectively. Handgrip strength, knee extensor strength, leg extensor power, stepping and maximum walking speed were significantly higher in non-homebound than in homebound men and women. These results suggest that the physical fitness levels of homebound were lower than those of non-homebound, but no difference was observed in the PA levels between homebound and non-homebound.

RELATIONSHIP BETWEEN DAILY STEPS AND PHYSICAL FITNESS IN COMMUNITY-DWELLING ELDERY / 体力科学

The purpose of this study was to examine the association between the pedometer-determined steps per day and physical fitness in order to evaluate the usefulness of the pedometer-determined physical activity to help individuals meet the recommended exercise target level of the Ministry of Health, Labour and Welfare (MHLW). The subjects consisted of 222 men and 172 women aged 71 years in community-dwelling elderly. The subjects wore a pedometer for 7 consecutive days to measure daily steps. The functional capacity was assessed based on the Tokyo Metropolitan Institute of Gerontology Index of Competence (TMIG-IC) and self-reported performance of tasks (stair-climbing and chair-rising). Physical fitness tests included handgrip strength, knee extensor strength, leg extensor power, stepping, one-leg standing time with eyes open and maximal walking speed at 10 m. The men and women took on average 6,561±2,907 and 6,329±2,451 steps/day, respectively. Our subjects seemed to be highly functioning elderly, because the total scores of TMIG-IC (maximum : 13 scores) were on average 12 for men and women. The average of steps/day was significantly correlated with stair-climbing, chair-rising and knee extensor strength in men and women, and with body weight, body mass index (BMI), percent body fat (%Fat) and leg extensor power in women. The BMI and %Fat levels were significantly lower while the handgrip strength and knee extensor strength were significantly higher in women who attained to the level of the pedometer-determined physical activity as recommended by the MHLW.The present study suggests that both men and women who take a lot of steps on a daily basis tend to demonstrate excellent leg strength and thus have a good ability to perform the tasks of daily living. In addition, the degree of obesity tends to be lower in women who regularly take a lot of steps. In addition, the number of daily steps taken has been recognized to be linked to gender, and such a link has also been suggested to be stronger in women than in men.

CHANGE OF FOREARM MUSCLE OXYGEN CONSUMPTION IN PEDIATRIE KIDNEY TRANSPLANT PATIENTS / 体力科学

The aim of the present study is to clarify the improvement of peripheral muscle oxygen consumption after successful renal transplantation. We investigated change of forearm (brachioradial muscle) muscular oxygen consumption in chronic renal failure children before and after renal transplantation. by using near-infrared spectroscopy.Oxygen consumption of brachioradial muscle was increased significantly after succesful renal transplantation. And half recovery time of brachioradial muscle oxygenation in arterial occlusion and exercise were decreased after renal transplantation.These results suggest that increased muscular blood flow and increased oxidative generation of ATP might contribute to the increased oxygen turn over after renal transplantation.

EFFECTS OF PHYSICAL ACTIVITY ON AGE-RELATED DECLINE IN OXYGEN DELIVERY TO WORKING MUSCLES / 体力科学

The purpose of this study was to determine the age and habitual physical activity on re-oxygenation time in working muscles following maximal cycling exercise (CycEXmax). Twelve sedentary middle-aged (50±6), 13 sedentary elderly (66±3), 13 active middle-aged (53±5), and 20 active elderly (67±5) were evaluated the half re-oxygenation time (T1/2 reoxy) as an index of oxygen delivery, using near-infrared spectroscopy at the vastus lateralis (VL) and lateral head of the gastrocnemius (LG) after CycEXmax. T1/2 reoxys at VL and LG were significantly greater in the elderly subjects than in the middle-aged subjects in both sedentary and active groups. T1/2 reoxys at VL and LG of the active group were smaller than those of the sedentary group, regardless of age. The results of this study suggest that habitual physical activity may attenuate age-related prolongation in T1/2 reoxy in working muscles although ageing delay T1/2 reoxy in working muscles.

BLOOD FLOW AFTER CONTRACTION OF SHORT DURATION REACHES ITS PEAK BY 3^rd CARDIAC CYCLE / 体力科学

The purpose of this study was to elucidate how long it takes to reach peak blood flow after muscle contractions in consideration of the cardiac cycle. Seven healthy female subjects performed two successive dynamic plantar flexions of 1-s duration at 30, 50 and 70% of maximal voluntary contraction (MVC). Based upon the blood flow response after a single contraction, we set up intervals during two successive contractions each corresponding to 10% (10 I), 30% (30 I) and 50% (50 I) of the time required to reach peak blood flow. Upon cessation of contraction, the popliteal artery blood flow (Qpa) increased progressive, beat-by-beat increase and peaked by the 5^th cardiac cycle, for all conditions. The highest peak blood flow among the cardiac cycle was at 3^rd cycle in overall data. Peak Qpa values reached after exercise did not differ among intervals, whereas peak Qpa value attained after exercise was significantly greater in 50 and 70%MVC than 30%MVC (p<0.05). The result indicates that the augmentation of the Qpa after exercise with short duration differed with the exercise intensity but the timing for reaching peak post-exercise value did not differ in terms of the number of cardiac cycles.

Pattern of deoxygenation in vastus lateralis and rectus femoris muscles during a ramp-loaded cycling / 体力科学

The purpose of this study was to compare changes in oxygenation in the Vastus Lateralis (VL) and Rectus Femoris (RF) muscles during a ramp-loaded bicycle exercise. Twelve healthy males participated in the experiment. The test consisted of a leg arterial occlusion at rest and a ramp-loaded exercise (20 watts/min) using a bicycle ergometer until exhaustion. The changes in deoxygenation in each muscle was measured by near infrared spectrometer (NIRS) . The probes of NIRS were placed on VL and RF approximately 12 cm above the right knee. Oxy-Hb/Mb signals from NIRS were calculated as 100% at rest, with 0 % being the lowest value during the leg arterial occlusion. Pulmonary gas exchanges (VE, VO<SUB>2</SUB>, VCO<SUB>2</SUB>) were measured with an expiratory gas analyzer. In 10 subjects, muscle oxygenation level in VL decreased linearly until the deoxygenation limiting point (DOLP) -the point in exercise at which the deoxygenation rate decreases noticeably. However, in 2 subjects, the DOLP was not detected, and the muscle oxygenation level decreased linearly until exhaustion. The muscle oxygenation level in RF also decreased linearly until 70%VO<SUB>2</SUB>max, although the deoxygenation rate was smaller than that in VL. Thereafter, the muscle oxygenation level in RF continued to decrease until exhaustion. No DOLP was found in any subjects in RF. Compared with the muscle oxygenation level in RF at any points during the exercise, those in VL were lower until 90%VO<SUB>2</SUB>max (P<0.001) . However, the difference in muscle oxygenation levels between VL and RF at exhaustion was not noted. This study indicated that the patterns of deoxygenation in VL and RF during a ramploaded bicycle exercise were different.

The relationship between endurance time and fatigue factors at varying intensities in handgrip isometric exercise / 体力科学

The purpose of the present study was to investigate the relationship between endurance time and fatigue factors at varying intensities of handgrip isometric exercise. Seven subjects performed isometric contractions at 10%, 30% and 50% of maximum voluntary contraction (MVC) sustained to exhaustion. Continuous changes in high-energy phosphates and muscle oxygen content (oxy-Hb/Mb) in the forearm flexor muscle were measured by <SUP>31</SUP>P magnetic resonance spectroscopy (<SUP>31</SUP>P-MRS) and near infrared spectroscopy (NIRS), respectively. The endurance time to exhaustion was 963±236 (mean±S. D.), 209±41.9 and 95.3±13.6s at 10%, 30% and 50%MVC, respectively, From the onset of exercise at each %MVC, both PCr and oxy-Hb/Mb fell and Pi (H<SUB>2</SUB>PO<SUB>4</SUB>-) rose linearly with time, whereas intracellular pH remained relatively constant at resting values during the early phase. Thereafter, intracellular pH showed a linear decline. The rates of pH decline were 0.03±0.02, 0.22±0.14 and 0.51±0.17 pHunit/min, while the rates of H<SUB>2</SUB>PO<SUB>4</SUB>- increase were 20.9±19.3, 118±48.9 and 434±242 (% of resting) /min at 10%, 30% and 50%MVC, respectively. There were correlations between the changes in endurance times to exhaustion and the rates of pH decline (r= -0.58--0.87) and H<SUB>2</SUB>PO<SUB>4</SUB>- increase (r=-0.37--0.74, (n=7) ) at each intensity of exercise. In particular, significant correlations (p<0.05) between endurance time and the rate of pH decline were found at both 10% and 30%MVC. These results suggest that muscle fatigue (endurance time) at each intensity in handgrip isometric exercise is closely correlated with the rate of pH decline.

Effects of local cooling and heating in the triceps surae muscles during sustained isometric contraction / 体力科学

A study was conducted to examine activity patterns of surface electromyograms (EMGs) in the triceps surae muscles (medial gastrocnemius, MG ; lateral gastrocnemius, LG ; soleus, SOL) during isometric contraction in plantar flexion (60% MVC, 20% MVC) after immersion in water at three different temperatures. Seven healthy male subjects were immersed in water at 2-3°C (ICE), 19-21°C (MID), and 40-42°C (HOT) . The results of the study are summarized as follows :<BR>1) In the MG and LG, there was a slight increase in the rate of integrated electromyograms (IEMGs) in the MG (the main agonist muscle) . However, the rate of increase in the LG, which is the synergistic muscle, was much greater than that in the MG when contraction was sustained at 60% MVC. Therefore, the activity pattern suggests that muscle activity in the LG compensates for that in the MG.<BR>2) The IEMGs of the SQL with sustained contraction, increased significantly after immersion in HOT and MID, but the IEMGs decreased after immersion in ICE. These results suggest that the recruitment threshold in slow-type motor units should increase during sustained isometric contrac-tion in ICE.<BR>As illustrated above, the activity of the LG increased to compensate for that of MG. In the SQL, muscle activity with sustained contraction decreased in ICE. These results suggest that control mechanisms of the central nervous system might play an important role in the associated movement of the triceps surae muscles.

Relationships of intracellular pH to oxygenated hemoglobin/myoglobin and to phosphate compounds in active muscle during forearm exercise / 体力科学

The purpose of this study is to find a key to clarifying the mechanism of lactic acid production during exercise. Five healthy men performed the grip and wrist flexion exercises at different occasions. Exercise intensities were increased by 5% MVC (maximum voluntary contraction force) per minute from 10% MVC. Intracellular pH, oxygenated hemoglobin/myoglobin (Oxy-Hb/Mb), inorganic phosphate (Pi), and phosphocreatin (PCr) in forearm flexor muscles were measured by <SUP>31</SUP>P-MRS and NIRS. The lowest Oxy-Hb/Mb concentrations during the grip and wrist flexion exercises were 40.7± 8.86% (average±SE) and 15.4 ± 2.26%, respectively. These results suggest that oxygen remain sufficient in the muscles at least during the grip exercise. Intracellular pH dropped as exercise intensity rose above 25% MVC for the grip and above 10% MVC for the wrist flexion exercise. These results support the idea that oxygen deficiency is not the only cause for lactic acid production during exercise. On the other hand, intracellular pH fell with either negative or positive relations to Pi/PCr ratio, Pi, and PCr in each exercise. These results support the suggestion that the main causes of lactic acid production during exercise are the changes in ADP, Pi, and PCr.