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Saunders N. Whittlesey and Joseph Hamill

An alternative to the Iterative Newton-Euler or linked segment model was developed to compute lower extremity joint moments using the mechanics of the double pendulum. The double pendulum model equations were applied to both the swing and stance phases of locomotion. Both the Iterative Newton-Euler and double pendulum models computed virtually identical joint moment data over the entire stride cycle. The double pendulum equations, however, also included terms for other mechanical factors acting on limb segments, namely hip acceleration and segment angular velocities and accelerations Thus, the exact manners in which the lower extremity segments interacted with each other could be quantified throughout the gait cycle. The linear acceleration of the hip and the angular acceleration of the thigh played comparable roles to muscular actions during both swing and stance.

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Darryn S. Willoughby

This study examined 12 wk of resistance training and cystoseim canariensis supplementation on serum levels of myostatin and follistatin-like related gene (FLRG) and muscle strength and body composition. Twenty-two untrained males were randomly assigned to a placebo (PLC) or myostatin binder (MYO) group in a double-blind fashion. Blood was obtained before and after 6 and 12 wk of training. PLC and MYO trained thrice weekly using 3 sets of 6 to 8 repetitions at 85% to 90% 1 repetition maximum. MYO ingested 1200 mg/d of cystoseim canariensis. Data were analyzed with 2-way ANOVA. After training, total body mass, fat-free mass, muscle strength, thigh volume/mass, and serum myostatin and FLRG increased for both groups (P < 0.05); however, there were no differences between groups (P > 0.05). Twelve wk of heavy resistance training and 1200 mg/d of cystoseim canariensis supplementation appears ineffective at inhibiting serum myostatin and increasing muscle strength and mass or decreasing fat mass.

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Kensaku Suei, Leslie McGillis, Randy Calvert and Oded Bar-Or

We assess relationships among muscle endurance, strength, and explosiveness in forty-eight 9.6- to 17.0-year-old males divided into 3 maturational groups (Tanner Stages I, II-IV, and V). Peak torque during isometric knee extension and flexion was averaged to reflect strength. Mechanical power in the Sargent vertical jump was taken as explosiveness, and total work in the Wingate test reflected muscle endurance. Correlations (3 groups combined) among the variables, expressed in absolute terms, were r = .82 to .92, but only -.11 to .70 when expressed per body mass or lean thigh size. These correlations were distinctly lower in the Tanner V boys than in the 2 less-mature groups, which may suggest that specialization into discrete muscle performance characteristics does not occur before late puberty.

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Emmanuel Van Praagh, Nicole Fellmann, Mario Bedu, Guy Falgairette and Jean Coudert

This study was done to determine the extent to which body composition accounts for differences in anaerobic characteristics between 12-year-old girls and boys. Peak leg power (PP), mean leg power (MP), percent body fat, fat free mass (FFM), and lean thigh volume (LTV) were determined by various tests. Pubertal stages and salivary testosterone concentration (in boys) were used to assess sexual maturation. Laboratory anaerobic indices were compared with performances in two running tests. Blood samples were taken for lactate determination. Absolute PP and MP outputs were similar in both sexes and were better correlated with LTV in girls, whereas in boys both PP and MP were highly correlated with FFM. Although nonsignificant gender difference in lean tissue was observed, PP and MP when corrected for LTV were significantly greater in boys than in girls. Factors other than the amount of lean muscle mass should be considered in explaining the gender differences in PP and MP in early pubertal children.

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Ugo H. Buzzi and Beverly D. Ulrich

The purpose of this study was to examine the dynamic stability of two groups of children with different dynamic resources in changing contexts. The stability of the lower extremity segments of preadolescent children (8–10 years old) with and without Down syndrome (DS) was evaluated as children walked on a motorized treadmill at varying speeds. Tools from nonlinear dynamics, maximum Lyapunov exponent, and approximate entropy were used to assess the behavioral stability of segmental angular displacements of the thigh, shank, and foot. Our results suggest that children with DS show decreased dynamic stability during walking in all segments and that this might be a consequence of inherently different subsystem constraints between these groups. Differences between groups also varied, though not uniformly, with speed, suggesting that inherent differences could further constrain the behavioral response to changing task demands.

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Hwang-Jae Lee, Won Hyuk Chang, Sun Hee Hwang, Byung-Ok Choi, Gyu-Ha Ryu and Yun-Hee Kim

The purpose of this study was to examine age-related gait characteristics and their associations with balance function in older adults. A total of 51 adult volunteers participated. All subjects underwent locomotion analysis using a 3D motion analysis and 12-channel dynamic electromyography system. Dynamic balance function was assessed by the Berg Balance Scale. Older adults showed a higher level of muscle activation than young adults, and there were significant positive correlations between increased age and activation of the trunk and thigh muscles in the stance and swing phase of the gait cycle. In particular, back extensor muscle activity was mostly correlated with the dynamic balance in older adults. Thus, back extensor muscle activity in walking may provide a clue for higher falling risk in older adults. This study demonstrates that the back extensor muscles play very important roles with potential for rehabilitation training to improve balance and gait in older adults.

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Kristin Taraldsen, Beatrix Vereijken, Pernille Thingstad, Olav Sletvold and Jorunn L. Helbostad

The aim of the study was to investigate the precision of estimated upright time during one week in community-dwelling older adults after hip fracture when monitoring activity for different numbers of consecutive days. Information about upright time was collected by thigh-worn accelerometers during 7 consecutive days in 31 older adults (mean age 81.8 years ± 5.3) 3 months after hip-fracture surgery. Mean time in upright position, including both standing and walking, was 260.9 (±151.2) min/day. A cutoff value of half an hour was used to provide recommendations about number of recording days. Large variability between participants between days, as well as a nonconstant within-participant variability between days indicates that at least 4 consecutive days of recording should be used to obtain a reliable estimate of upright time for individual persons. However, at a group level, one day of recording is sufficient.

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Yusuke Osawa, Yasumichi Arai, Yuko Oguma, Takumi Hirata, Yukiko Abe, Koichiro Azuma, Michiyo Takayama and Nobuyoshi Hirose

This study investigated the relationships between muscle echo intensity (EI), physical activity (PA), and functional mobility in 108 Japanese (88–92 years). We measured EI and muscle thickness (MT) at the midpoint of the anterior superior iliac spine and patella using B-mode ultrasound. Light and moderate-to-vigorous PA (LPA and MVPA) were assessed with a triaxial accelerometer. The timed up and go (TUG) test was used to measure for functional mobility. EI, but not MT, was significantly associated with both TUG scores (β = 0.17, p = .047) and MVPA (β = –0.31, p = .01) when adjusted by potential confounders. However, association between EI and TUG disappeared after adjusted for MVPA. Meanwhile, MVPA was significantly associated with TUG scores independent of EI (β = –0.35, p < .001). Although EI of anterior thigh muscles might be a weaker predictor of functional morbidity than MVPA, it is a noninvasive and practical approach for assessing muscle quality in the very old.

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Jonisha P. Pollard, William L. Porter and Mark S. Redfern

Euler angle decomposition and inverse dynamics were used to determine the knee angles and net forces and moments applied to the tibia during kneeling and squatting with and without kneepads for 10 subjects in four postures: squatting (Squat), kneeling on the right knee (One Knee), bilateral kneeling near full flexion (Near Full) and bilateral kneeling near 90° flexion (Near 90). Kneepads affected the knee flexion (p = .002), medial forces (p = .035), and internal rotation moments (p = .006). Squat created loading conditions that had higher varus (p < .001) and resultant moments (p = .027) than kneeling. One Knee resulted in the highest force magnitudes and net moments (p < .001) of the kneeling postures. Thigh-calf and heel-gluteus contact forces decreased the flexion moment on average by 48% during Squat and Near Full.

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Scott J. Black, Michael L. Woodhouse, Stephen Suttmiller and Larry Shall

The effects of hip position on thigh electromyographic (EMG) activity and knee torque were evaluated. Twenty-four recreational athletes (12 males and 12 females) volunteered to participate. Subjects were tested isokinetically at 30°/s in sitting and supine positions both concentrically and eccentrically during knee flexion and extension. Gravity-corrected torques (N·m) were obtained for all tests. EMG amplitude (mV) was collected via surface electrodes. Torque values were significantly greater (p<.05) for knee flexion in the sitting position when compared to the supine. EMG activity did not change relative to hip position but typically increased (p<.05) during concentric trials. Knee extension torque and EMG activity did not change during sitting or supine positions. Results indicated that the sitting position had statistically significant advantages over the supine position for producing greater hamstring torque and maintaining similar levels of EMG output during isokinetic knee flexion.