This study aimed to determine the different changes of muscle hardness between the human rectus femoris (RF) and vastus intermedius muscle (VI) after maximal knee extension exercise. Eight healthy men (23.0±2.6 years) performed maximal isometric contraction (IM), concentric contraction (CC), and eccentric contraction (EC) exercises of the knee extensors. Muscle hardness (i.e., strain ratio, SR) and thickness in the proximal, middle, and distal parts of RF and VI were measured by using strain elastography before and after exercises. The rates of change between the values were calculated as values before exercise 100%. For VI, a significant main effect in “part” was found in IM and EC exercises in SR. Results show that SR in the distal part (IM, 89.0±27.2%; EC, 78.2±26.9%) was significantly lower than that in the middle part (IM, 105.5±34.3%; EC, 91.8±30.4%) for each exercise (p<0.05). However, no significant main effect in “part” was found in SR of RF in any exercise. A significant main effect was found in “part” in muscle thickness of RF in the IM exercise. Also, muscle thickness in the distal part (104.5±7.7%) was significantly higher than that in the proximal part (102.5±4.3%) for each exercise (p<0.05). These results suggest that changes of muscle hardness and thickness in the proximal, middle, and distal parts of the human rectus femoris and vastus intermedius muscle after maximal knee extension exercises are different.
Flexibility is an important factor of physical fitness to prevent sports injuries. However, the best timing to improve flexibility during the growth and development period in children has been unclear. To compare the acute effects of static stretching on flexibility between school-grade children in the growth and development period, we measured the hip joint flexion range of motion (RoM) by using straight leg raising (SLR) before and after static stretching (6 exercises, 15 seconds, 2 sets) in 50 young male children aged 7 to 13 years (the second grade of elementary school to the first grade of junior high school). The RoM in SLR significantly increased after stretching versus that before stretching in all subjects. This positive improvement of RoM was statistically significant among all grade levels. Notably, the change rate in RoM after stretching was significantly greater in the fourth grade of elementary school than in the other grades. The rate of height increase during the past year was lower in students from the fourth grade than in students from the second grade of elementary and the first grade of junior high school. These results suggest that flexibility training is more effective during the slow-down period of growth and development in young male children.
The aim of the present study was to determine the effects of expiratory effort on the magnitude and low-frequency components of force variability during submaximal isometric knee extension (IKE). Eight subjects performed 5-s IKE of the dominant leg at the intensity of 10% of maximal voluntary contraction (10% MVC). During the IKE, the subjects performed one of three forced expirations (FEs) of different effort levels. The three effort levels of FE were 0% effort (normal breathing, FE0), 50% effort (FE50) and 100% effort (FE100). In the expiratory phase of each IKE, the amplitude of the force variability was quantified by the coefficient of variation (FCV), and the low-frequency components of the force variability were evaluated by calculating the peak power values of the filtered force signal (F) and rectified EMG signal with high-pass filtering (rEMGH) of the vastus lateralis muscle. The cross-correlation between F and rEMGH was also calculated. FCV was significantly higher in FE100 than in FE0 and FE50 (p < 0.01). The peak power values of F and rEMGH was significantly higher in FE100 than in FE0 (p < 0.05). Cross-correlation between F and rEMGH with the latter preceding the former was observed in each FE condition. These results suggest that FE with maximal effort (FE100) increased not only the absolute amount of force variation but also low-frequency oscillatory components of force and EMG and that low-frequency oscillations of motor unit firing may be responsible for the increase in force variation induced by FE.
Ankle exercises are useful for preventing deep vein thrombosis, as they increase venous blood flow velocity. The cause for the increased venous blood flow velocity during ankle exercises may be the skeletal-muscle pump, but the mechanism is not clearly understood. The purpose of this study was to investigate the effects of the dorsiflexion angle and gastrocnemius muscle contraction on venous blood flow velocity during ankle exercises and to investigate the mechanism of the increase in venous blood flow velocity. The blood flow velocity in the popliteal vein, ankle joint angle, and surface electromyographic activity of the gastrocnemius muscle were measured at rest and during ankle exercises in the prone position in young healthy volunteers. The significant increase in venous blood flow velocity was observed during dorsiflexion phase, max dorsiflexion and during planter flexion phase. The peak venous blood flow velocity was different in each subject and classified into four types. The correlations of venous blood velocity to ankle joint angle and with the surface electromyographic activity of the gastrocnemius muscle were not statistically significant. These findings suggest that venous blood flow velocity increases not only during plantar flexion and dorsiflexion.
Habitual aerobic exercise decreases arterial stiffness, a risk factor for cardiovascular disease, and increases aerobic exercise capacity. Exercise habits can be difficult to maintain over time. We sought to determine if the prospect of participating in a sports tourism event (mountain climbing) helped older adults maintain increased aerobic exercise capacity and decreased arterial stiffness after a supervised training program. Forty community-dwelling middle-aged and older individuals were divided into training (n=20) and control (n=20) groups. The training group participated in six weeks of face-to-face exercise intervention (walking, 60%–75% of age-predicted maximal heart rate, 35–50 min/day, 1 day/week) and was additionally offered home-based walking (45 min/day, 2–4 days/week). During the same period, the control group was asked not to change their lifestyle. In the last session of the exercise program, we announced a mountain climbing event planned for six months in the future. The participants were encouraged to maintain their exercise habits leading up to the event. Arterial stiffness (brachial-ankle pulse wave velocity) and maximal oxygen uptake were measured before and after the six-week intervention and two weeks before the mountain climbing event. In the training group, arterial stiffness decreased, and maximal oxygen uptake increased after the intervention; these improvements were successfully maintained until the mountain climbing event. These parameters did not change significantly in the control group. Sports tourism may motivate older adults to maintain their exercise habits after a supervised training program.