The aim of this study was to investigate longitudinal changes in rate for development (RFD) during the early, late, and whole phases, and to determine whether early RFD is exhibited in response to the improvement of explosive force production in training throughout the competitive season. Fifteen male jumpers participated in personal training according to the training cycle (Semi-annual two-cycle periodization model) of their team. The early, late and average RFD along with peak force during isometric single-leg press with a knee angle of 115° were measured. The measurement was performed during the pre-season (January or March) and post-season (September or November). Based on comparison between the two measurements, it was found that 10 participants displayed improved performance in the major jump event. The average RFD increased significantly for all participants (p = 0.02, d = 0.67). Participants who achieved their personal best had seen a significant increase in early RFD (p = 0.03, d = 0.84). In the contrast, late RFD (all participants; p = 0.06, d = 0.54, participants who achieved personal best; p = 0.07, d = 0.65) and peak force (all participants; p = 0.31, d = 0.27, participants who achieved personal best; p = 0.15, d = 0.50) did not show significant changes. These results suggested that changes in early, late, and average RFD varied respectively. Moreover, early RFD was found to be the best indicator that reflects improved jumping performance through explosive force production compared to late RFD, average RFD, and peak force.

Purpose of this study was to examine the recovery process of delayed onset muscle soreness, jump performance, force to contact with the ground and lower limbs movement after intensive jump exercise (IJE), and the relationships between muscle soreness, changes of jump performance and lower limbs movement. Nine males who have experience in special jump exercise participated in this study voluntarily. For the measurement, subjective investigation of the muscle soreness, drop jump performance using a 30 cm high box [jump height, contact time and drop jump index (jump height / contact time)], ground reaction force and movements of lower limbs. This measurement was carried out before IJE (Pre), and at 4 hours (P4), 24 hours (P24) and 72 hours (P72) after IJE. Main results are as follows ; at the time of P24 when intense muscle soreness appeared, significant jump height decreases and contact time increases were shown, and the jump index decreased markedly. This decrease of performance correlated to the change of knee and ankle joint movements during the eccentric phase. At P4, for a subject who felt strong muscle soreness, the decrease of jump height and jump index were considerable. At P72, most subjects recovered to the levels of jump height and contact time to the Pre level. The findings reveal that the jump performances are related to the degree of delayed onset muscle soreness.

The purpose of this study was to investigate the influence of physiological factors which effect oxygen kinetics and energy system contribution on the power of Wingate test (WT), with focusing on the difference of aerobic capacity. Twenty three male track and field athletes (sprinters, long distance runners and decathletes) performed the WT on electromagnetic-braked cycle ergometer. The applied resistance was 7.5% of body weight, and the duration was 60 seconds. Moreover, aerobic capacity (maximal oxygen uptake [VO₂max]) was determined by an incremental test, and anaerobic capacity (maximal accumulated oxygen deficit [MAOD]) was determined by a supramaximal constant load test. The oxygen uptake during each test was recorded by a breath-by-breath method. The participants were divided into two group which was high VO₂max group (High group; n = 11) and low VO₂max group (Low group; n = 12). In the results, although the VO₂max was significantly higher in the High group, the MAOD was not significantly different between two groups. The oxygen uptake during WT was significantly higher in the High group, and the accumulated oxygen deficit during WT was significantly higher in the Low group. The aerobic contribution was significantly higher in the High group than in the Low group. In contrast, the anaerobic contribution was significantly higher in the Low group than in the High group. These results suggest that by the difference of aerobic capacity, aerobic and anaerobic energy supply contribution was different in WT.

The purpose of this study was to investigate the relationship among torque, motion of lower limbs during the take-off phase and muscle strength of lower limbs. Subjects were 12 male track and field athletes who had a top record of 6.84±0.41 m. Several variables of the 12 subjects, such as displacement, velocity, angle and angular velocity, and maximum torque of the knee and hip joints during the take-off phase, were obtained from film analysis and measurement of lower limb strength by Biodex.
The main results were as follows:
1. Subjects who had a lower angular velocity of the take-off knee joint after landing showed a lower decreasing ratio of velocity during the takeoff phase.
2. There was a significant relationship between records for the long jump and hip flexion torque of the take-off leg during the last part of the take-off phase (r=-0.678, P<0.05) .
3. Subjects who showed a higher value of hip flexion torque of their free leg during the last part of the take-off phase showed lower take-off angles.
4. There was a significant relationship between knee extension strengths (60, 180, 300 deg/s) and knee joint angles at the middle of the take-off phase (r=0.700 P<0.01, r=0.672 P<0.05, r=0.751 P<0.01) .
5. Subjects who maintained a larger knee angle for their take-off leg indicated a decrease in knee extension torque of their take-off leg during the last part of the take-off phase.
6. Subjects who showed higher hip extension strength made the transition to hip flexion torque of the take-off leg from the middle to the last part of the take-off phase.
From these results, it can be seen that knee extension strength is important for efficient take-off, and hip joint torque is one of the factors that influences one's record in the long jump.

The purpose of this study was to compare hip and knee joint extension torque and the activity of eight muscles around the hip and knee joints during three squat exercises with different movements.
Ten male athletes performed three different squats (Normal squat : NS, Knee push squat : KPS, Hip drive squat : HDS) . KPS is the type of squat which emphasizes knee joint movement without moving the hip joint position back and forth. On the other hand, HDS is the type of squat which emphasizes hip joint movement, while keeping the knee joint position fixed. Kinematic and kinetic variables such as angle, angular velocity, net torque and power of the joints of the lower extremity were calculated during the descending and ascending phase of each squat. At the same time, surface electrodes were placed on eight muscles of the lower extremity, and %iEMG was also calculated during the same phases.
During the descending phase, Elector spinae muscle activity and hip joint extension torque was significantly greater for HDS than KPS. Rectus femoris and Vastus lateralis muscle activity was significantly greater for KPS than HDS. In addition, KPS showed significantly greater knee joint extension torque than HDS and NS. At the ascending phase, Elector spinae, Glueus maximus and Biceps femoris muscle activity, and hip joint extension torque was significantly greater for HDS than KPS and NS. Rectus femoris muscle activity and knee joint extension torque was significantly greater for KPS than HDS and NS.
These results suggest that HDS is effective for selectively training the hip extensor, and KPS is effective for training the Rectus femoris muscle.

The purpose of this study was to compare joint torque and the activity pattern of eight muscles crossing the ankle, knee and hip joints during three kinds of squats with different speeds (Slow, Normal, Quick) . Ten male athletes performed squats at three different speeds. Variables such as net torque and power about the joint were calculated during the descending and ascending phase of each squat. At the same time, surface electrodes were placed over the eight lower extremity muscles, and %iEMG was also measured during the ascending phase of each squat.
During the descending phase, the activity of elector spinae (ES), Gluteus maximus (Gmax), Gluteus medius (Gmed), Rectus femoris (RF), Biceps femoris (BF), Adductor longus (AL), and Vastus lateralis (VL) muscles was significantly greater for Quick squats than Normal and Slow squats, whereas during the ascending phase, activity was significantly greater for Quick and Normal squats than for Slow squats. Mean torque around the hip joint increased significantly when switching from Slow to Quick squats in the descending phase; and during the ascending phase, mean torque was sig nificantly greater for Quick and Normal squats than for Slow squats. The median frequency (MDF) of an electromyogram of the Gmax was significantly lower for Normal squats than for Quick squats ; and in the ascending phase, the MDF of the BF was significantly lower for Normal squats than for Quick and Slow squats.
Quick squats use the stretch-shortening cycle so that the load around the Gmax may increase. Although mean muscle activity for Slow squats was smaller than for Nomal squats, MDF was greater. MDF was greater for Slow squats suggesting that Slow squats mobilize type-II fibers in spite of the slow movement ; and is, therefore, useful for strength training with low risk of injury.

The squat is used for strength training of the hip and knee joint muscles. The weight to be lifted is important for multi-joint movement like a squat, because weight differences are thought to directly affect joint load. The purpose of this study is to compare the activity of eight muscles crossing the ankle, knee and hip joints during three kinds of squats with different loads (60%, 75% and 90% of 1RM) . Eight male athletes performed squats with three different loads. Variables such as net torque, power and work about the joint were calculated only during the ascending phase of each squat. At the same time, surface electrodes was placed over the eight lower extremity muscles, and %iEMG was also calculated during the ascending phase of each squat. Elector spinae and Biceps femoris muscle activity of 90% was significantly greater than at 60%. Gluteus maximus muscle activity at 90% was significantly of 75% and 60%. Mean torque and work on the hip joint increased significantly as load increased from 60% and 75% to 90%. For the knee, mean torque increased significantly from 60% to 90%. These results that a heavy weight like 90% of 1RM used in squat exercise increases the load on the hip joint extensor muscles.

The purpose of this study was to investigate the effects of different sitting postures, by change of seat height, on lower extremity muscle activation and maximum power during explosive bicycle pedaling exercises. The subjects performed 5 sec maximum pedaling exercises at three different seat heights.‘High’ seat height was defined as 95% of leg length, ‘Middle’ was 90% and‘Low’ was 85%.
The results were summarized as follows: A) At 3 revolutions, maximum power at‘High’ was significantly higher than that at‘low’. B) Pelvic angle at‘High’ was significantly higher than that at‘Low’. C) The maximum extension angle of the knee joint was a significantly high value in descend. ing order of‘High’, ‘Middle’ and‘Low’. D) mEMG of the Erector spinae and Biceps femoris at‘High’ was significantly higher than that at‘Low’. E) At‘High’, there was a significant correlation between maximum power of 3 revolutions and mEMG in the Gluteus maximus. In addition, maximum power at 3 revolutions tended to correlate with mEMG in the Biceps femoris and Vastus lateralis.
These results suggest that in explosive pedaling exercises, different sitting postures by change of seat height, have different influences on hip extension muscle activation and maximum power.

A study was conducted to investigate the relationships among changes of joint torque of the lower limbs, sprint ability such as sprint speed, stride length and stride frequency in 400 m running, and muscular endurance of the lower limbs. Subjects were 11 male track and field athletes who had a 400m running time of 48.75±1.32s. The experiment was composed of videotaping sprint form at 160 m and 360 m points during 400 m running, and measuring muscular endurance of hip and knee flexion and extension using Cybex NormTM.
The main results were as follows:
1) There was a significant relationship between 400 m running time and ability to maintain a higher running speed at the 360 m point.
2) Running speed, stride length and stride frequency decreased significantly at the 360 m point.
3) Subjects who showed a smaller decrease in stride frequency at the 360 m could maintain higher running speed.
4) Subjects who showed smaller decrease in maximal joint torque of the lower limbs at the 360 m could maintain a higher running speed.
5) There was a significant relationship between an increase in support time and decrease in maximal joint torque of hip extension for the recovery leg.
6) Ability to maintain joint torque during 400 m running was influenced by muscular endurance of the lower limbs.
These results suggest that the ability to maintain torque needed for higher performance in 400 m running is influenced by muscular endurance of the lower limbs.