In this study, the difference between the effects of “power-up type” and “bulk-up type” strength training exercise was investigated by analyzing parameters such as structural and functional adaptations in the neuromuscular system. Eleven subjects were divided into power-up and bulk-up groups. The power-up group comprised five male subjects who performed 5 sets at 90% of one repetition maximum (1 RM) with a 3-min rest between sets (repetition method) . The bulk-up group comprised six male subjects who performed 9sets at 80-60-50%, 70-50-40%, and 60-50-40% of 1 RM with rest intervals between sets of either 30 s or 3 min (interval method) . Both groups performed isotonic knee extension exercise twice a week for 8 weeks. The power-up group showed a lower rate of improvement than the bulk-up group in terms of cross-sectional area (CSA) of the quadriceps femoris at levels 30%, 50% and 70% from the top of the femur, and also in average isokinetic strength (Isok. ave. ; 180 deg/s, 50 consecutive repetitions) . However, the power-up group showed a greater rate of improvement in 1 RM, maximal isometric strength (Isom. max), and maximal isokinetic strength (Isok. max ; 60, 180, 300 deg/s) . Furthermore, the rate of reduction in strength over 50 consecutive isokinetic repetitions decreased in the bulk-up group. On the other hand, the power-up group showed no significant changes in the above throughout the entire training program. These results indicate that the characteristics of the two types of training exercise are as follows : (1) power-up exercise is effective mainly for improving muscular strength and anaerobic power, and (2) bulk-up exercise is effective mainly for improving hypertrophy and anaerobic endurance. These findings support the idea that “power-up type” and “bulk-up type” strength training exercises should be applied appropriately according to the training aim.

The purpose of the present study was to determine the change in total excess volume of CO₂output (CO₂excess) due to bicarbonate buffering of lactic acid produced during exercise and change in swimming performance following resistance training for 8 weeks in competitive swimmers. Ten healthy university competitive swimmers were assigned to either a resistance training and swimming training group (COMBINE: N=5) or a swimming training only group (SWIM: N=5) . Muscle mass was measured using magnetic resonance imaging (MRI) . CO₂excess and blood lactate concentration were measured during incremental exercise on a cycle ergometer and swimming performance was measured during competition. COMBINE showed a significantly higher percentage change in muscle mass (11.1±4.5%) than SWIM (3.5±2.5%) . The percentage change in CO₂excess, CO₂excess per body weight (CO₂excess/BW) and CO₂excess/BW per blood lactate accumulation (CO₂excess/BW/ΔLa) during exercise was significantly higher in COMBINE (107.3±60.1, 102.6±56.8, 59.1±37.7%, respectively) than in SWIM (42.5±10.0, 42.9±10.4, 13.4±22.4%, respectively) . The percentage change in swimming performance was significantly higher in COMBINE (2.2±1.8%) than in SWIM (-2.0±3.6%) . A negative correlation between percentage change of muscle mass and percentage change of CO₂excess/BW/ ΔLa (SWIM: r=-0.993, P<0.01, COMBINE: r=-0.744, P>0.05) was found. It was suggested that combined swim and resistance training resulted in greater increases in the bicarbonate buffering system (CO₂excess/BW/ΔLa) . However, increases in muscle mass may have subsequently caused a relative decrease in the contribution of the bicarbonate buffering system.

In this study, the effect of moderate endurance training on muscle morphological properties of human thigh muscles and isokinetic strength was examined. Five sedentary females carried out a training program of 30 min./day, 3 times a week for a ten-week period. The load requirement was set to 60% of maximal aerobic capacity (Vo₂max) of the subjects. In the determination of muscle cross-sectional areas (CSAs) by MRI, longitudinal sections were first imaged, and ten axial images along the length of femur were taken before and after the endurance training. Muscle CSA and mus-cle volume of knee extensors (KE), flexors (KF), and adductors (AD) were calculated, using the ten axial images. Vo₂max was significantly increased after endurance training (14.6%, p<0.01) . Muscle CSA in KE was significantly increased at the ten levels of femur length. There were also significant increases at seven levels of femur length after endurance training in KF (p<0.05, and 0.01) . Percentage increase of msucle CSA in KE and KF were 10.9 to 16.5% and 7.7 to 15.8%, respectively. Although the muscle volume of KE, KF, and AD was significantly increased, no change in fat volume was observed after endurance training. Isokinetic knee extension and flexion peak torque and peak torque per unit of muscle CSA at three angular velocities (30, 180, and 300 deg/sec) didn't show significant changes. These results suggest that muscle hypertrophy induced by moderate endurance training has no effect on muscle strength.

To evaluate the changes in muscle energetics following NaHCO₃ intake, we measured the phosphorus-31 nuclear magnetic resonance (³¹P NMR) spectra of human muscle in vivo during exercise. Seven male subjects performed two trials, a NaHCO₃ (Alka, Tr.) and a NaCI trial (Cont. Tr.), on two occasions. ³¹P NMR spectra were obtained serially during leg-elevating exercises. Before and during exercise, the intracellular phosphocreatine (PCr), inorganic phosphate (Pi) and pH were determined from the NMR spectra. The decrease of intracellular pH during exercise showed a tendency to be inhibited by NaHCO₃ intake, and the intracellular pH at the end of the exercise was 6.69 for Alka. Tr, and 6.51 for Cont. Tr. The decline of the PCr/ (PCr+Pi) ratio during exercise was not influenced by NaHCO₃ intake. The PCr/ (PCr+Pi) ratio was related exponentially to the intracellular pH. A remarkable decline of PCr/ (PCr+Pi) ratio occurred until the intracellular pH fell to about 6.7, but did not decrease below that. It was suggested that the intake of NaHCO₃ could decrease the rate of fall in the intracellular pH during exercise, and that the PCr store could be influenced by the intracellular pH when the pH was above 6.7, but not below that level.

A study was conducted to investigate using ³¹P NMR the relationship between the total excess volume of CO₂ output (CO₂ excess) due to bicarbonate buffering of lactic acid produced in exercise and the decrease of intracellular pH during incremental exercise. Five sprinters and 5 joggers performed incremental exercise to exhaustion on an bicycle ergometer. The values of CO₂ excess and CO₂ excess per body weight (CO₂ excess/W) were not different between the sprinters (2388±659ml, 36.7±8.5 ml·kg^-1) and the joggers (2275±278ml, 40.0±6, 3ml·kg^-1) . Below the ventilatory threshold (VT), from VT to the respiratory compensation point (RCP), and above RCP, the V_od2-V_co2 slopes were not different between the sprinters and the joggers, respectively (0.95±0.05 vs 0.95±0.06, 1.21±0.11 vs 1.30±0.14, 1.69±0.24 vs 1.76±0.18) . However, the joggers showed significantly higher CO₂ excess/W per blood lactate accumulation (ΔLa) in exercise (CO₂ excess/W/ΔLa, 5.34±0.32ml·kg^-1·mmol^-1·l^-1) than the sprinters (4.50±0.14ml·kg^-1·mmol^-1·l^-1) . The decrement of intracellular pH during incremental exercise showed a tendency to be smaller in joggers (0.63±0.18 pH unit) than in sprinters (0.83±0.10 pH unit), although there was no significant difference between the two groups. The values of CO₂ excess/W/ΔLa were correlated with the decrease of intracellular pH (r=-0.792, p<0.01) . It is suggested that CO₂ excess/W/ΔLa reflects the efficiency of the bicarbonate buffering system, and could be an important factor influencing the decrease of intracellular pH due to lactate production.

In this study, the effect of moderate endurance training on muscle morphological properties of human thigh muscles and isokinetic strength was examined. Five sedentary females carried out a training program of 30 min./day, 3 times a week for a ten-week period. The load requirement was set to 60% of maximal aerobic capacity (Vo₂max) of the subjects. In the determination of muscle cross-sectional areas (CSAs) by MRI, longitudinal sections were first imaged, and ten axial images along the length of femur were taken before and after the endurance training. Muscle CSA and mus-cle volume of knee extensors (KE), flexors (KF), and adductors (AD) were calculated, using the ten axial images. Vo₂max was significantly increased after endurance training (14.6%, p<0.01) . Muscle CSA in KE was significantly increased at the ten levels of femur length. There were also significant increases at seven levels of femur length after endurance training in KF (p<0.05, and 0.01) . Percentage increase of msucle CSA in KE and KF were 10.9 to 16.5% and 7.7 to 15.8%, respectively. Although the muscle volume of KE, KF, and AD was significantly increased, no change in fat volume was observed after endurance training. Isokinetic knee extension and flexion peak torque and peak torque per unit of muscle CSA at three angular velocities (30, 180, and 300 deg/sec) didn't show significant changes. These results suggest that muscle hypertrophy induced by moderate endurance training has no effect on muscle strength.

We investigated the muscle energetics using ³¹P nuclear magnetic resonance (³¹P NMR) spectroscopy, muscle cross-sectional area by magnetic resonance imaging (MRI), isokinetic strength, maximal anaerobic power and 40-sec maximal cycling test (40 seconds power) in All Japan soccer players (JPN: n=6), Olympic and Youth representatives (OL: n=6), and Japan Soccer League players (JSL: n=5) . There was no significant difference in muscle energy metabolism measured by ³¹P NMR between the JPN and the OL or JSL players at rest, during exercise, or in the recovery period. The total muscle cross-sectional area was significantly larger in the JPN players than in the OL players at the upper (70%) and the middle (50%) parts of the thigh (p<0.05) and than in the JSL players in the upper (p<0.01), middle (p< 0.05), and lower (30%) parts (p<0.01) . The isokinetic strength in left leg extension at 180 deg/sec was significantly greater in the JPN players than in the OL players (p<0.05) . Muscle strength was also greater in extension of both legs at 450 deg/sec (left p<0.05, right p<0.01) in the JPN players than in the JSL players. The maximum anaerobic power was significantly greater in the JPN players than in the OL players (p<0.05) and the JSL players (p<0.05), and the anaerobic power per kilogram of body weight was significantly higher in the JPN players than in the JSL players (p<0.01) . There was no significant difference in the 40 seconds power among the three groups. These results suggest that the JPN players have greater muscle power than the OL or JSL players because of the differences in the muscle mass.

The purpose of this study was to prove the hypothesis that the effect of strength training is memorized and reinforced by retraining. Untrained university-age men participated in this training program. The retraining leg was subjected to 5 weeks of isometric training, 17 weeks of detraining and 5 weeks of retraining in knee extension. The contralateral training leg was subjected to 5 weeks of isometric training during the same period as the retraining phase of the retraining leg. Maximal isometric torque of knee extension increased after the 5-week training and remained at the trained level during the 17week detraining period. Torque gain by retraining of the retraining leg was 2.6 times greater than that of the contralateral training leg. These changes in isometric torque corres-ponded with changes in iEMG of the vastus lateralis. The cross-sectional area of the quadriceps femoris muscle did not change with training. Results support the hypothesis that the effect of strength training is memorized and reinforced by retraining. In addition, results show that these adaptations would be explained by recruitment and rate coding of motor units.