Contralateral versus ipsilateral protective effect against muscle damage of the elbow flexors and knee extensors induced by maximal eccentric exercise.

The present study compared the ipsilateral repeated bout effect (IL-RBE) and contralateral repeated bout effect (CL-RBE) of the elbow flexors (EF) and knee flexors (KF) for the same interval between bouts to shed light on their mechanisms. Fifty-two healthy sedentary young (20-28 years) men were randomly assigned to the IL-EF, IL-KF, CL-EF, and CL-KF groups (n = 13/group). Thirty maximal eccentric contractions of the EF were performed in IL-EF and CL-EF, and 60 maximal eccentric contractions of the KF were performed in IL-KF and CL-KF, with a 2-week interval between bouts. Changes in muscle damage markers such as maximal voluntary contraction (MVC) torque, muscle soreness, and plasma creatine kinase activity, and proprioception measures before to 5 days post-exercise were compared between groups. Changes in all variables were greater (p < 0.05) after the first than second bout for all groups, and the changes were greater (p < 0.05) for the EF than KF. The changes in all variables after the second bout were greater (p < 0.05) for the CL than IL condition for both EF and KF. The magnitude of the average protective effect was similar between CL-EF (33%) and CL-KF (32%), but slightly greater (p < 0.05) for IL-EF (67%) than IL-KF (61%). These demonstrate that the magnitude of CL-RBE relative to IL-RBE was similar between the EF and KF (approximately 50%), regardless of the greater muscle damage for the EF than KF. It appears that the CL-RBE is more associated with neural adaptations at cerebrum, cerebellum, interhemispheric inhibition, and coricospinal tract, but the IL-RBE is induced by additional adaptations at muscles.

Latent Transition Analysis of Motor Development Patterns in Preschoolers.

In-group heterogeneity is often neglected during investigations of motor development patterns in children. Moreover, the variation in motor development patterns over time has seldom been examined. In this work, 1884 three-year-old preschoolers were selected from a panel study conducted in Taiwan called the National Longitudinal Study of Child Development and Care. A confirmatory factor analysis was applied to analyze the construct validity of the assessments of motor development used for these children. A latent profile analysis and latent transition analysis (LTA) were sequentially applied to clarify their motor development patterns at the ages of three and four years and their transitions between these two ages. The following findings were obtained: (1) The motor development assessment had good validity. (2) Considerable heterogeneity regarding motor development in preschoolers was observed, in which four and three subgroups displaying distinct levels of mastery with respect to their gross and fine motor skills were identified at the ages of three and four years, respectively. (3) From age three to age four, a large proportion of the preschoolers exhibited improvements or retentions in both gross and fine motor skills, whereas some of the preschoolers were classified into subgroups displaying "gross motor retention and fine motor progression," "gross motor progression and fine motor retention," "gross motor retention and fine motor regression," and "gross motor regression and fine motor progression." Few preschoolers exhibited "general motor regression." The present results suggest that there were considerable heterogeneous groups in the motor development in preschoolers in the middle of early childhood, and this phenomenon has rarely been addressed in former studies. The LTA results implied that effective interventions should be given sequentially to preschoolers in subgroups whose motor development presented regression and retention tendencies.

Effect of Load Carriage Lifestyle on Kinematics and Kinetics of Gait.

Backpacks are commonly worn by many people for multiple purposes. This study investigated the effects of habitual wearing of backpacks on lower limb kinematics and kinetics. Fourteen participants were recruited for analysis. All participants performed four randomly assigned scenarios, including running and walking at speeds of 3.5 and 1.5 m/s, respectively, with and without load carriage. The motion analysis system and force plate were used to investigate the lower limb kinematics and kinetics. A paired sample t-test was performed for statistical measurement with a significance level of α = .05. The results indicated that active force, breaking force, impact peak, loading rate, active peak, maximum braking, hip flexion, and hip range of motion were substantially higher under load carriage conditions than under walking condition, however, time to peak was lower. Conversely, during load carriage running, active force, braking impulse, time to peak, ankle plantarflexion, and ankle range of motion were all higher than those during running. Carrying a backpack weighing 10% of the body weight induced different foot strike patterns at both speeds; during load carriage walking, the hip tended to flex more; whereas, during load carriage running, the ankle tended to flex more. In conclusion, human body seems to adopt different gait strategies during load carriage walking and running. That is, the hip strategy is used during walking, while the ankle strategy is used during running.

Changes in Insulin Sensitivity and Lipid Profile Markers Following Initial and Secondary Bouts of Multiple Eccentric Exercises.

An acute bout of eccentric exercise affects insulin sensitivity and lipid profile, but how the magnitude of muscle damage affects them is not clear. We compared changes in blood insulin sensitivity and lipid markers after the first (EC1) and second (EC2) eccentric exercise bouts. Fifteen sedentary young men performed arm, leg and trunk muscle eccentric exercises, and repeated them 2 weeks later. Fasting blood samples were taken before, 2 h and 1-5 days after each exercise bout to analyze plasma creatine kinase (CK) activity, serum glucose (GLU), insulin, homeostasis model assessment (HOMA), triacylglycerols (TG), total (TC) and low- (LDLC) and high-density lipoprotein cholesterol (HDLC) concentrations as well as TC/HDLC ratio. Changes in these measures were compared between bouts and relationships to peak plasma CK activity were analyzed. Plasma CK activity increased (p < 0.05) after EC1 (peak: 101,668 ± 58,955 IU/L) but not after EC2. The magnitude of changes in GLU (peak after EC1: 26 ± 10% vs. EC2: 7 ± 6%), insulin (46 ± 27% vs. 15 ± 8%), HOMA (86 ± 48% vs. 24 ± 15%), TC (-20 ± 5% vs. -6 ± 4%), TG (-32 ± 11% vs. -6 ± 3%), LDHC (-47 ± 15% vs. -12 ± 9%), HDLC (35 ± 26% vs. 7 ± 4%), and TC/HDLC ratio (-139 ± 13% vs. -11 ± 7%) were significantly greater after EC1 than EC2. Peak plasma CK activity was significantly (p < 0.05) correlated with the peak changes in blood insulin sensitivity and lipid markers for the combined data of EC1 and EC2. These results suggest that the greater the magnitude of muscle damage, the greater the magnitude of changes in the insulin sensitivity to a negative direction and lipid markers to a positive direction.

Suprapostural effects of light digital touch on the modulation of postural sway can be modified by fingertip sensitivity.

We investigated whether the suprapostural effects of light digital touch on the modulation of postural sway can be modifiedby fingertip sensitivity. To achieve this, we recruitedthree types of athleteswith various fingertip sensitivity levels, including swimmers (high sensitivity), basketball players (intermediate sensitivity), and rowers (low sensitivity). We recorded the center of pressure (COP) excursions in 21 swimmers (20.57±0.42years), 22 basketball players (20.79±0.75years), and 22 rowers (20.32±0.49years) during light-touch (LT) and precision light-touch (PLT) conditions. In the LT conditions, participants touched a force plate while standing with their feet shoulder-width apart. In the PLT condition, participants were instructed to precisely touch a fixed point on the plate. Compared to the LT condition, the execution of the PLT condition significantly reduced the magnitude of COP excursion in the AP axis for all groups. This effect was most pronounced in swimmers, followed by basketball players, then rowers. These findings suggest that the suprapostural effects of precision light-touch on postural control can be modified as a function of fingertip sensitivity.

Effects of Low-Impact Dance on Blood Biochemistry, Bone Mineral Density, the Joint Range of Motion of Lower Extremities, Knee Extension Torque, and Fall in Females.

The effect of low-impact dance on blood metabolites, the joint range of motion (ROM) of the lower extremities, knee extension torque, bone mass density (BMD), the number of falls, and the confidence to perform daily activities (Modified Falls Efficacy Scale [MFES]) was examined in older sedentary women (age: 59 ± 4 years) before and after a 16-week intervention. Results showed that the average score for the MFES, some parameters of blood chemistry, and joint ROM were significantly improved after low-impact intervention. In addition to improvements in blood lipids and body fat percentages, the increases shown in the parameters regarding the lower extremities may contribute to confidence in performing common daily activities in older women, although the number of falls did not significantly differ between the two groups during the 16-week period.

Effects of light touch on postural sway and visual search accuracy: A test of functional integration and resource competition hypotheses.

People often multi-task in their daily life. However, the mechanisms for the interaction between simultaneous postural and non-postural tasks have been controversial over the years. The present study investigated the effects of light digital touch on both postural sway and visual search accuracy for the purpose of assessing two hypotheses (functional integration and resource competition), which may explain the interaction between postural sway and the performance of a non-postural task. Participants (n=42, 20 male and 22 female) were asked to inspect a blank sheet of paper or visually search for target letters in a text block while a fingertip was in light contact with a stable surface (light touch, LT), or with both arms hanging at the sides of the body (no touch, NT). The results showed significant main effects of LT on reducing the magnitude of postural sway as well as enhancing visual search accuracy compared with the NT condition. The findings support the hypothesis of function integration, demonstrating that the modulation of postural sway can be modulated to improve the performance of a visual search task.

The effects of low-impact dance on knee torque and lower extremity mobility in middle-aged and older women.

BACKGROUND: Although low-impact dance is one of the most prevalent exercises in older persons, little is known about its effects on knee torque and range of motion (ROM) in lower extremity joints. PURPOSE: The aim of this study was to examine the effects of low-impact dance on knee torque and lower extremity joint ROM in older women. METHODS: Twenty-six low-impact dancers and 12 physically inactive individuals comprised the dance group (DG) and the control group (CG), respectively. The knee extension torque, knee and ankle ROMs, and bone mineral density in calcanei were measured for all participants. RESULTS: Several ROMs of the lower extremity joints in the dominant leg, ankle inversion, plantarflexion, and dorsiflexion were significantly higher in the DG than in the CG (p < .05). In addition, the ankle inversion of the nondominant leg in the DG was also significantly higher than that in the CG. The knee extension torque of the nondominant leg in the DG was significantly higher than that in the CG (p < .05). CONCLUSION: Although this study did not focus on the efficacy of a particular intervention type, the results showed that low-impact dance can help achieve higher lower extremity ROM and knee torque values than attained by inactive individuals. It is hoped that this exposition of positive benefits will encourage further studies related to the effect of low-impact dance intervention on reducing fall risk.

The influence of ball velocity and court illumination on reaction time for tennis volley.

The he purpose of this study is to examine the effects of ball velocity, court illumination, and volley type on the reaction time (RT) of a tennis athlete for a volley stroke. Eights cases with two different ball velocities (high and low), two volley types (forehand and backhand ) and two court illumination levels (dark and bright) were studied. The 30 participating subjects consisted of 18 male and 12 female college tennis athletes (age: 24 ± 3.2 yr), with a United States Tennis Association (USTA) ranking above 2.5. In order to ensure the validity of real-world correlations, the experiments were designed to simulate real competition situations. Reaction times were measured for volley strokes in response to different approaching ball velocities (high: 25.05 ± 0.37 m/s and low: 17.56 ± 0.92 m·s(-1)) for several volley types (forehand and backhand) and court illumination levels (55649 ± 4292 lux and 363.24 ± 6.53 lux on the court). During the tests, the signals from an electromyogram sensor and a 3-axis accelerometer (± 50 g) were recorded using an NI DAQ card (NI PXI-6251) and then analyzed to determine reaction time (RT), premotor reaction time (PRT), and motor reaction time (MRT) through the LabVIEW system. Subsequent 3-way ANOVA analysis indicated no RT, PRT, or MRT interaction between ball velocity, volley type and illumination. The ball velocity and illumination parameters did affect RT and PRT values significantly with p < 0.05, no significant variation in MRT was observed across any implemented experimental conditions. All experimental results indicate that ball velocity and illumination levels strongly affect the value of PRT, but have no significant effect on the value of MRT, the changes in RT were dominated by PRT. Key pointsRT can generally be divided into two components with the help of the electromyogram (EMG) signal - the premotor reaction time (PRT) and the motor reaction time (MRT).The purpose of this study is to examine the effects of ball velocity, court illumination level, and volley type on the reaction time (RT) of the tennis athlete for volley strokes.Results strongly suggest that changes in RT were dominated by PRT; in light of this correspondence, it is clear that the ability to sense visual stimuli may be enhanced by proper training and practice.

Changes in running economy following downhill running.

In this study, we examined the time course of changes in running economy following a 30-min downhill (-15%) run at 70% peak aerobic power (VO2peak). Ten young men performed level running at 65, 75, and 85% VO2peak (5 min for each intensity) before, immediately after, and 1 - 5 days after the downhill run, at which times oxygen consumption (VO2), minute ventilation, the respiratory exchange ratio (RER), heart rate, ratings of perceived exertion (RPE), and blood lactate concentration were measured. Stride length, stride frequency, and range of motion of the ankle, knee, and hip joints during the level runs were analysed using high-speed (120-Hz) video images. Downhill running induced reductions (7 - 21%, P < 0.05) in maximal isometric strength of the knee extensors, three- to six-fold increases in plasma creatine kinase activity and myoglobin concentration, and muscle soreness for 4 days after the downhill run. Oxygen consumption increased (4 - 7%, P < 0.05) immediately to 3 days after downhill running. There were also increases (P < 0.05) in heart rate, minute ventilation, RER, RPE, blood lactate concentration, and stride frequency, as well as reductions in stride length and range of motion of the ankle and knee. The results suggest that changes in running form and compromised muscle function due to muscle damage contribute to the reduction in running economy for 3 days after downhill running.