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.

Background The time courses of the joint elevation angles of the thigh, shank, and foot in one stride during walking can be well approximated by a “plane” in a triaxial space. This intersegmental coordination (IC) of the lower limb elevation angles is referred to as the planar covariation law. We examined the effects of exercise habituation and aging on the thickness of the IC plane of the lower limbs under sinusoidal speed changing conditions. Methods Seventeen sedentary young (SY), 16 active young (AY), and 16 active elderly (AE) adults walked on a treadmill in accordance with a sinusoidal speed changing protocol at 120, 60, and 30 s periods with an amplitude of ± 0.56 m·s−1. Motion of the lower limbs from the sagittal direction was recorded to calculate the elevation angles of the lower limbs. When the best-fit IC plane was determined, the smallest standard deviation of the IC plane was considered as the anteroposterior gait variability of the lower limbs. The coefficient of variance of the step width was also quantified to evaluate the lateral step variability (CVSW). Results The standard deviation of the IC plane was significantly greater in the order of SY, AY, and AE, regardless of the sinusoidal wave periods of the changing speed. The CVSW was not significantly different among the three groups. Conclusions Exercise habituation influences anteroposterior gait variability of the lower limbs, but not lateral step variability, even in young adults. Given these, gait adaptability for sinusoidal speed changes does not always decline with aging. Trial registration UMIN000031456 (R000035911; registered February 23, 2018).

Kinematic parameters during throwing were analyzed to examine whether the absence of runup before ball release or ball graspability was associated with ball velocity acquisition process in 33 participants. Three-dimensional coordinates were measured using a motion analysis system with eight infrared cameras with a sampling rate of 250 Hz. The captured motion data were computed to calculate the kinematic parameters. Path analysis, a structural equation modeling technique, was applied to the obtained kinematic parameters to clarify the "strength" and "direction" of the interrelationship among the observed parameters because it can detect the relationship of each parameter in the complicated theoretical model. When throwing small graspable softballs "without" run-up, the velocity of the center of the body mass influenced the ball velocity. However, in that case, a greater backward trunk tilt with a longer acceleration distance is necessary to acquire greater ball velocity. When throwing large non-graspable dodgeballs with and without run-up and/or throwing small graspable softballs "with" run-up, the horizontal velocity of the thrower's center of the body mass positively affected the ball velocity via pull distance due to the acceleration distance of the ball and increased step length.The non-graspable dodgeball accelerated with a shorter pull distance in the lateral direction,

Objective: A U-shaped relationship between energy cost of walking (Cw; J·kg-1·m-1) and walking speed indicates that there is a specific speed minimizing the Cw, called economical speed (ES). It is mostly slower in older adults than young adults; however, effects of leg length on the ES have been ignored. We investigated the effects of aging and exercise habituation on the normalized ES by the leg length (nor-ES). Moreover, the diversity in the stride length (SL) and step frequency (SF) against sinusoidal speed change (SSC) at 30-s and 180-s periods with ±0.56 m･s-1 among sedentary young (SY), active young (AY), and active elderly (AE) adults was also quantified. Results: The ES was significantly faster in the following sequence: AY, SY, and AE, whereas nor-ES was faster in the AY and SY than in the AE (no difference was found between AY and SY). Delayed SL and preceding SF were observed at the 180-s SSC in the young adults only. Collectively, greater delay and/or precedence of SL-SF combinations against SSC may reflect locomotive flexibility for passive speed change during walking. The nor-ES was slowed by aging; however, it was not influenced by exercise habituation, at least, in young populations.