ABSTRACT
A study was conducted to investigate the mechanism of bone atrophy in various strains of inbred mice under the influence of tail-up suspension. Nine inbred strains of mice (NZB/N, NZW/N, AKR/N, Balb/C, C 57 BL, C 3 H/He, A/J, DBA, CBA/N) aged six weeks were used. Each strain was divided randomly into two groups, a suspension group (SG; n=5) and a control group (CG; n=5) . The suspension group were etherized and suspended with an elastic bandage. After one week, the tibiae were removed and their bone weights were measured using an electric balance (Metler; AE 240) . Their length was also measured with a vernier caliper. In all strains, body weight in the SG was significantly lower than that in the CG. From the bone weight and length in the CG, bone growth in the NZB/N, AKR/N, NZW/N and C3H/He strains was considered to be higher than in the other strains. On the other hand bone growth in the DBA, A/J, Balb/C, and CBA/N strains were lower than in the others. The absolute value of bone weight in the SG was significantly smaller than that in the CG in six strains (NZB/N, C 57 BL, A/J, NZW/N, C 3 H/He, Balb/C) . However in the DBA strain, the absolute value of bone weight in the SG was significantly higher than that in the CG.<BR>From the results of this investigation we suggest that the mechanism of normal bone growth is not the same as the mechanism of bone atrophy induced by tail-up suspension.
ABSTRACT
Oxidation of lactate at rest (RE, n=4), or after short strenuous exercise (EX, n=6) was investigated in rats. Food and water were given ad libitum before experiment. In EX, rats ran to exhaustion at the speed of 80-100 m·min<SUP>-1</SUP>. Immediately after exercise, 4 μCi of (U-<SUP>14</SUP>C) lactate was injected into aorta through an indwelling catheter. In RE, (U-<SUP>14</SUP>C) lactate was injected into the rats at rest. Expired gas was collected by a Brooks type bottomless chamber on treadmill belt for 120 min. In EX, exercise duration was 109±18 sec (mean±SE), and maximum blood lactate concentration after the exercise was 23.7±2.1 mM (mean±SE) . Cumulative percent recovery of <SUP>14</SUP>C as <SUP>14</SUP>CO<SUB>2</SUB> for 120 min was 48.5±2.8% for EX and 61.7±0.9% for RE (mean±SE) . Significant difference was found between these two rates (p<0.01) . After 50 min of recovery, mean volume of <SUP>14</SUP>CO<SUB>2</SUB> expired per min in RE was significantly greater than that in EX (p<0.01) . Mean volume of <SUP>14</SUP>CO<SUB>2</SUB> expired per min per VCO<SUB>2</SUB> in RE was always greater than that in EX, and significant difference was found at 7.5 min of recovery (p<0.01) . It is concluded that although the rate of recovery of <SUP>14</SUP>C as <SUP>14</SUP>CO<SUB>2 </SUB>after exercise is lower than that at rest, the major pathway of lactate metabolism after short strenuous exercise is oxidation.
ABSTRACT
The influence of daily physical exercise on oxygen utilizing capacity of working muscle investigated by means of measureing lactate threshold (LT) during progressive treadmill running from the comparison between soccer group (S group: N=12, 11.9±0.1 years of age) and control group (C group ; N=14, 11.8±0.1 years of age) . LT<SUB>1</SUB> was determined as the point where blood lactate concentration (La) increased from rest level, and LT<SUB>2</SUB> was determined by the gradient, La/VO<SUB>2</SUB>. body weight<SUP>-1</SUP> (2 mM/10 ml. kg<SUP>-1</SUP>, min<SUP>-1</SUP>) .<BR>LT<SUB>1</SUB> and LT<SUB>2</SUB> in S group were significantly higher than those in C group expressed with absolute and relative values of VO<SUB>2</SUB> (1. min<SUP>-1</SUP>, ml. kg<SUP>-1</SUP>. min<SUP>-1</SUP>, % VO<SUB>2</SUB>max) . No significant differences in La, ventilation responses, and heart rate at the point of LT<SUB>1</SUB> and LT<SUB>2</SUB> were observed between S and C group, La showed slight decrease and was kept at lower level in S group with increase of VO<SUB>2</SUB>, compared with C group. On the contrary, La in C group began to increase at lower level of VO<SUB>2</SUB>. From our previous longitudinal study of LT in non-athletic children, we observed that LT shifted to lower level with growth. It was sugesed that La curve of S group, such shift had not occurred. Differences of these patterns in VO<SUB>2</SUB> and La between athletic children and non-athletic children were similar to those observed in adults athletes and non-athletes.<BR>In conclusion it was supposed that sufficient daily physical training in 10-12 year of age might increase oxygen utilizing capacity of leg working muscle during running exercise.
ABSTRACT
The relationships between running performances (200 m running time and 5-min run) and VO<SUB>2</SUB>max, Lactate Threshold (LT), or percent fat were investigated on 11-12-year old boys. Subjects were 21 control boys (group C) and 21 soccer boys (group S) . Mean 200 m running time in group S was significantly better than that in group C. Mean distance of 5-min run in group S was significantly longer than that in group C. No significant difference was found between mean running speed of 5-min run and mean speed at exhaustion in LT experiment. In group C, 200 m running time correlated significantly with VO<SUB>2</SUB>max. In group S, faster runners showed higher peak post 200 m run lactate concentration. 5-min run correlated significantly with VO<SUB>2</SUB>max for group C, group S and all subjects combined. LT correlated significantly with 200 m running time and 5-min run. No significant relation was found between running petformances and percent fat. It is suggested that VO<SUB>2</SUB>max and LT determine, in part, boy's running performances, but percent fat do not.
ABSTRACT
Ventilation threshold (VET), threshold of decompensated metabolic acidosis (TDMA) and lactate threshold (LT<SUB>1</SUB>, LT<SUB>2</SUB>) were investigated during incremental bicycle exercise for 20 boys (11.7±0.1 years) and 10 girls (11.2±0.2 years) .<BR>Maximum oxygen uptake (VO<SUB>2</SUB>max) was measured by treadmill running. There was significant difference between boys and girls in VO<SUB>2</SUB>max per body weight, but no signif-icant difference per LBM. Mean values of each threshold (% peak VO<SUB>2</SUB>) were as follows. VET was 53.3±2.2%, TDMA was 69.0±2.2%, LT<SUB>1</SUB>was 51.8±2.2% and LT<SUB>2</SUB>was 72.8±2.2%. These values were not higher than those of previous adult's data. There was no significant difference in lactate and ventilatory parameters between boys and girls, except LT<SUB>2</SUB>and LT<SUB>4</SUB>mM.<BR>In conclusion, it seems that no difference is seen in lactate and ventilatory responses between 9-12 year boys and girls. VET and TDMA by bicycle exercise could be estimated by ventilatory responses in prepubertal children.