Economical and preferred walking speed using body weight support apparatus with a spring-like characteristics.

BACKGROUND: A specific walking speed minimizing the U-shaped relationship between energy cost of transport per unit distance (CoT) and speed is called economical speed (ES). To investigate the effects of reduced body weight on the ES, we installed a body weight support (BWS) apparatus with a spring-like characteristics. We also examined whether the 'calculated' ES was equivalent to the 'preferred' walking speed (PWS) with 30% BWS. METHODS: We measured oxygen uptake and carbon dioxide output to calculate CoT values at seven treadmill walking speeds (0.67-2.00 m s- 1) in 40 healthy young males under normal walking (NW) and BWS. The PWS was determined under both conditions on a different day. RESULTS: A spring-like behavior of our BWS apparatus reduced the CoT values at 1.56, 1.78, and 2.00 m s- 1. The ES with BWS (1.61 ± 0.11 m s- 1) was faster than NW condition (1.39 ± 0.06 m s- 1). A Bland-Altman analysis indicated that there were no systematic biases between ES and PWS in both conditions. CONCLUSIONS: The use of BWS apparatus with a spring-like behavior reduced the CoT values at faster walking speeds, resulting in the faster ES with 30% BWS compared to NW. Since the ES was equivalent to the PWS in both conditions, the PWS could be mainly determined by the metabolic minimization in healthy young males. This result also derives that the PWS can be a substitutable index of the individual ES in these populations.

Regular change in spontaneous preparative behaviour on intra-abdominal pressure and breathing during dynamic lifting.

PURPOSE: Intra-abdominal pressure (IAP) and breathing behaviour are important preparative pre-lifting actions for functional stability during lifting. This study aimed to examine spontaneous changes in the peak rate of IAP development (Rate-IAP), peak IAP (Peak-IAP), the time of Rate- and Peak-IAP occurrence and respiratory volume in response to dynamic load lifting. METHODS: Eleven healthy men performed quick dynamic deadlifting using 30, 45, 60 and 75% of the isometric maximal lifting effort (iMLE). IAP was measured using an intrarectal pressure transducer. The spontaneous respiratory volume was calculated from air flow data using pneumotachography. The lifting motion onset was determined from the hip joint motion using an electrogoniometer. RESULTS: From 30 to 75% of the iMLE, Rate-IAP occurred early from 2 ± 28 to -179 ± 16 ms (P < 0.01), whereas Peak-IAP occurred late from 165 ± 31 to 82 ± 23 ms (P = 0.12) relative to the lifting motion onset. Rate-IAP increased from 224 ± 47 to 507 ± 69 mmHg/s (P < 0.01), whereas Peak-IAP increased from 37 ± 8 to 90 ± 11 mmHg (P < 0.01) at 30-75% of the iMLE. Rate-IAP strongly correlated with Peak-IAP at each lifting load (r = 0.94-0.97). Relative to the resting tidal volume, the inspiratory volume during pre-lifting significantly increased above 60% of the iMLE, whereas expiratory volume significantly decreased at all lifting loads. CONCLUSIONS: Preparative pre-lifting behaviours alter IAP and breathing and are co-ordinated by the lifting load magnitude. These behaviours appear to be functionally important for dynamic lifting.

Association between knee extensor strength and EMG activities during squat movement.

PURPOSE: The present study aimed to clarify how the force-generating capability of quadriceps femoris (QF) is associated to its surface EMG activity during a body mass-based squat movement. METHODS: Isometric knee extension torque (KET) during maximal voluntary contraction and EMG activities of the rectus femoris and vastus lateralis muscles during a body mass-based squat movement were determined in 53 men and 48 women age 19-90 yr, including 18 frail elderly persons who used the long-term care insurance system. The rectified EMG signals during the squat movement were averaged and normalized as the relative value (%EMG(max)) to that during maximal voluntary contraction. The %EMG(max) values for rectus femoris and vastus lateralis were averaged and used as an index representing the level of muscular activities of QF during the squat movement (QF %EMG(max)). RESULTS: QF %EMG(max) was nonlinearly related to KET relative to body mass (KET/BM). Linear piecewise continuous regression analysis showed that there was a breakpoint of 1.9 N·m·kg(-1) in the relationship between the two variables. In individuals with KET/BM less than 1.9 N·m·kg(-1), QF %EMG(max) rapidly increased as KET/BM decreased. CONCLUSIONS: The current results indicate that the activity level of QF during a body mass-based squat movement is influenced by its force generation capability. For individuals with a KET/BM less than 1.9 N·m·kg(-1), body mass-based squat movement is considered to be a fairly high-intensity exercise. The breakpoint of 1.9 N·m·kg(-1) may be assumed to be a threshold level of knee extensor strength, which should be maintained for performing the activities of daily living without great difficulty.

Changes in intra-abdominal pressure and spontaneous breath volume by magnitude of lifting effort: highly trained athletes versus healthy men.

Intra-abdominal pressure (IAP) is closely related to breathing behavior during lifting. Abdominal muscles contribute to both IAP development and respiratory function. The purpose of this study was to examine whether spontaneous breath volume and IAP altered with increased isometric lifting effort, and to compare the effect of different abdominal muscle strengths on these parameters. Maximal IAP during the Valsalva maneuver (maxIAP) and maximal isometric trunk flexor strength were measured in 10 highly trained judo athletes (trained) and 11 healthy men (controls). They performed isometric lifting with 0 (rest), 30, 45, 60, 75, 90, and 100% of maximal lifting effort (MLE). Natural inspiratory and expiratory volumes were calculated from air-flow data immediately before and after the start of lifting. IAP, measured using an intra-rectal pressure transducer during lifting, was normalized by maxIAP (%maxIAP). Trained athletes had higher maxIAP and stronger trunk flexor muscles than controls. A significant main effect of lifting effort was found on %maxIAP and respiratory volume. An interaction (lifting effort by group) was found only for %maxIAP. No significant group main effect or interaction was found for respiratory volume. Inspiratory volume increased significantly from tidal volume to above 60 and 45% of MLE in trained athletes and controls, respectively. Expiratory volume decreased significantly from tidal volume at above 30% of MLE in both the groups. These results suggest that spontaneous breath volume and IAP development are coupled with increased lifting effort, and strong abdominal muscles can modify IAP development and inspiratory behavior during lifting.

Good maintenance of physical benefits in a 12-month exercise and nutritional intervention by voluntary, home-based exercise: a 6-month follow-up of a randomized controlled trial.

We assessed the maintenance of physical benefits in a 12-month exercise and nutritional intervention in postmenopausal women (55-75 years of age) after 6-month postintervention follow-up by voluntary, home-based exercise, and examined whether physical factors responded differently to high or low exercise frequency during the 6-month postintervention period. Forty-five women completed the 12-month intervention program, followed by 6-month cessation of intervention, and were compared with 19 matched controls. Twenty-one of the former exercisers reported that they continued exercise training at least 30 min at least 3 days/week (high-frequency exerciser, HFE), while the remaining 24 former exercisers reported that they had done exercise training at least 30 min twice per week or less during the postintervention follow-up (low-frequency exerciser, LFE). The following items were measured at baseline, 12, and 18 months: bone strength, CS-30 test, 10-m obstacle walk, whole-body reaction time, one-leg stance, and grip strength. After 6-month postintervention follow-up, the beneficial effect on bone was not fully maintained. These benefits in physical performance obtained in the 12-month intervention program, except one-leg stance, were fully maintained for 6 months by voluntary, home-based exercise. The gained benefit in one-leg stance was not fully maintained; LFE showed a significant decrease over the 6-month postintervention follow-up period, suggesting that continued exercise training of at least 30 min at least 3 days/week is required to maintain the balance benefit. These findings suggest that a continued exercise program of voluntary, home-based exercise may be effective to maintain the physical benefits of exercise intervention that may lower fracture risk in later life.

The effect of a 12-week combined exercise intervention program on physical performance and gait kinematics in community-dwelling elderly women.

This study aimed to determine if combined exercise intervention improves physical performance and gait joint-kinematics including the joint angle and dynamic range of motion (ROM) related to the risk of falling in community-dwelling elderly women. A 12-week combined exercise intervention program with extra emphasis on balance, muscle strength, and walking ability was designed to improve physical performance and gait. Twenty participants attended approximately two-hour exercise sessions twice weekly for 12 weeks. Participants underwent a physical performance battery, including static balance, sit and reach, whole body reaction time, 10 m obstacle walk, 10 m maximal walk, 30-second chair stand, to determine a physical performance score, and received quantitative gait kinematics measurements at baseline and in 12 weeks. Significant lower extremity strength improvement 13.5% (p<.001) was observed, which was accompanied by significant decreases in time of the 10 m obstacle walk (p<.05) and whole body reaction time (p<.001) in this study. However, no significant differences were seen for static balance and flexibility from baseline. For gait kinematics, in the mid-swing phase, knee and hip joint angle changed toward flexion (p<.01, p<.05, respectively). Ankle dynamic ROM significantly increased (p<.05) following exercise intervention. The plantar flexion angle of the ankle in the toe-off phase was increased significantly (p<.01). However, other gait parameters were not significantly different from baseline. These findings from the present investigation provide evidence of significant improvements in physical performance related to the risk factors of falling and safe gait strategy with a combined exercise intervention program in community-dwelling elderly women. The results suggest this exercise intervention could be an effective approach to ameliorate the risk factors for falls and to promote safer locomotion in elderly community-dwelling women.

Lower extremity function in terms of shock absorption when landing with unsynchronized feet.

The purpose of this study was to clarify the lower extremity function in terms of the shock absorption during unsynchronized-foot landings. The characteristics of the supination and pronation in the ankle joint at landing were investigated, assuming that the measurements of the impact force on the body could be demonstrated by the changes that occurred during 3 different landing motions: -unsynchronized-foot landings, synchronized-foot landings, and one-foot landings. Subjects jumped to the floor from 10-cm footstools 3 times for each type of landing. For the synchronized-foot landing, the rear foot angle was 92.2 degrees at the start of landing and did not change significantly from landing start to 100 msec. For the one-foot landing, rear foot angle was 95.1 degrees at the start of landing and decreased rapidly to 87.1 degrees by 75 msec, and then increased rapidly to 90.8 degrees by 140 msec. For the unsynchronized-foot landing, the rear foot angle was 93.8 degrees at the start of the landing, decreased rapidly to 88.0 degrees by 75 msec, and then increased rapidly to 89.9 degrees by 115 msec. It was clarified that the lower extremity function for the shock attenuation during landing with the unsynchronized-foot was similar to that with one-foot landings, and the lower extremity function for supporting the body after another foot landing was similar to that after the synchronized-foot landings in this study.