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.
Scott J. Black, Michael L. Woodhouse, Stephen Suttmiller and Larry Shall
Robert K. Jensen, Tina Treitz and Sylvie Doucet
The purpose of this study was to develop prediction equations to estimate mass, radius to the center of mass (CM), and principal moments of the segments during pregnancy. Nonlinear regression equations were determined for the lower trunk, upper trunk, and thigh. The third sampling month of a longitudinal study was used (Sample 1, n = 15). The nonlinear regressions were then used to predict segment inertias above and below the third sampling month (Sample 2, the remaining 74 measurements). For the remaining segments, body mass and segment lengths were used as predictor variables for mass, radius to CM, and radius of gyration about the centroidal axes. The remaining seven segments did not change substantially during pregnancy, and the means of the repeated measures were used for the simple linear regressions. Eighteen of the 28 regressions and all of the CM regressions were significant. With pregnant subjects it is recommended that these regressions be used if application of the elliptical cylinder model is not possible.
Maurice R. Yeadon, Pui W. Kong and Mark A. King
This study used kinematic data on springboard diving performances to estimate viscoelastic parameters of a planar model of a springboard and diver with wobbling masses in the trunk, thigh, and calf segments and spring dampers acting at the heel, ball, and toe of the foot segment. A subject-specific angle-driven eight-segment model was used with an optimization algorithm to determine viscoelastic parameter values by matching simulations to four diving performances. Using the parameters determined from the matching of a single dive in a simulation of another dive resulted in up to 31% difference between simulation and performance, indicating the danger of using too small a set of kinematic data. However, using four dives in a combined matching process to obtain a common set of parameters resulted in a mean difference of 8.6%. Because these four dives included very different rotational requirements, it is anticipated that the combined parameter set can be used with other dives from these two groups.
Scott Ross, Kevin Guskiewicz, William Prentice, Robert Schneider and Bing Yu
T o determine differences between contralateral limbs’ strength, proprio-ception, and kinetic and knee-kinematic variables during single-limb landing.
Hip, knee, and foot isokinetic peak torques; anterior/posterior (AP) and medial/lateral (ML) sway displacements during a balance task; and stabilization times, vertical ground-reaction force (VGRF), time to peak VGRF, and knee-flexion range of motion (ROM) from initial foot contact to peak VGRF during single-limb landing.
The kicking limb had significantly greater values for knee-extension (P = .008) and -flexion (P = .047) peak torques, AP sway displacement (P = .010), knee-flexion ROM from initial foot contact to peak VGRF (P < .001), and time to peak VGRF (P = .004). No other dependent measures were significantly different between limbs (P > .05).
The kicking limb had superior thigh strength, better proprioception, and greater knee-flexion ROM than the stance limb.
Keith R. Williams, Rebecca Snow and Chris Agruss
This study investigated changes in kinematics with fatigue during intercollegiate competition, a noncompetitive track run, and a constant speed treadmill run. To account for changes in kinematics resulting from speed differences, regression equations for each individual generated from nonfatigue data were used to predict rested kinematics for speeds matching those of the fatigue conditions. A factor analysis procedure grouped 29 kinematic variables into sets of independent factors, and both factor variables and individual variables were analyzed for changes with fatigue, which were minimal. Only one significant difference was found in the factor variables between nonfatigue and fatigue states. Comparisons of specific kinematic variables showed a significant increase in step length with fatigue, an increased maximal knee flexion angle during swing, and an increased maximal thigh angle during hip flexion. While fatigue did not result in marked changes in kinematics for the group as a whole, changes for individuals were at times large.
Lise Kronborg, Thomas Bandholm, Henrik Palm, Henrik Kehlet and Morten Tange Kristensen
Early mobilization following hip fracture surgery reduces medical complications and mortality, but may increase the risk of falling. The aim was to objectively measure the physical activity (time spent upright) the first week after hip fracture surgery and relate it to functional performance and fear of falling at discharge. The 24-hr upright time was measured for a median of six days using a thigh-worn accelerometer in 37 patients (mean 80 years ± 8.4) and increased from median 13 (IQR 6–31) min to 46 (11–107) min at day 7. More upright time at discharge was associated with less fear of falling (r = –.48, p = .01, n = 27), which also was associated with fast gait speed (r = –.50, p = .02, n = 23) and a faster Timed Up and Go test time (r = .54, p < .01, n = 22), indicating a need for further studies on motivation and limitations for more physical activity following hip fracture surgery.
Yuya Watanabe, Michiya Tanimoto, Akane Ohgane, Kiyoshi Sanada, Motohiko Miyachi and Naokata Ishii
The authors investigated the effects of low-intensity resistance training on muscle size and strength in older men and women. Thirty-five participants (age 59–76 yr) were randomly assigned to 2 groups and performed low-intensity (50% of 1-repetition maximum) knee-extension and -flexion exercises with either slow movement and tonic force generation (LST; 3-s eccentric, 3-s concentric, and 1-s isometric actions with no rest between repetitions) or normal speed (LN; 1-s concentric and 1-s eccentric actions with 1-s rests between repetitions) twice a week for 12 wk (2-wk preparation and 10-wk intervention). The LST significantly increased thigh-muscle thickness, as well as isometric knee-extension and -flexion strength. The LN significantly improved strength, but its hypertrophic effect was limited. These results indicate that even for older individuals, the LST can be an effective method for gaining muscle mass and strength.
Bradley C. Nindl, William J. Kraemer, Lincoln A. Gotshalk, James O. Marx, Jeff S. Volek, Jill A. Bush, Keijo Häkkinen, Robert U. Newton and Steve J. Fleck
Regional fat distribution (RFD) has been associated with metabolic derangements in populations with obesity. For example, upper body fat patterning is associated with higher levels of free testosterone (FT) and lower levels of sex-hormone binding globulin (SHBG). We sought to determine the extent to which this relationship was true in a healthy (i.e., non-obese) female population and whether RFD influenced androgen responses to resistance exercise. This study examined the effects of RFD on total testosterone (TT), FT, and SHBG responses to an acute resistance exercise test (ARET) among 47 women (22 ± 3 years; 165 ± 6 cm; 62 ± 8 kg; 25 ± 5 %BF; 23 ± 3 BMI). RFD was characterized by 3 separate indices: waist-to-hip ratio (WHR), ratio of upper arm fat to mid-thigh fat assessed with magnetic resonance imaging (MRI ratio), and ratio of subscapular to triceps ratio (SB/TRi ratio). Skinfolds were measured for the triceps, chest, subscapular, mid-axillary, suprailaic, abdomen, and thigh regions. The ARET consisted of 6 sets of 10 RM squats separated by 2-min rest periods. Blood was obtained pre- and post- ARET. TT, FT, and SHBG concentrations were determined by radioimmunoassay. Subjects were divided into tertiles from the indices of RFD, and statistical analyses were performed by an ANOVA with repeated measures (RFD and exercise as main effects). Significant (p < .05) increases following the AHRET were observed for TT (~25%), FT (~25%), and SHBG (4%). With multiple regression analysis, anthropometric measures significantly predicted pre- concentrations of FT, post-concentrations of TT, and pre-concentrations of SHBG. The SB/TRi and MRI ratios but not the WHR, were discriminant for hormonal concentrations among the tertiles. In young, healthy women, resistance exercise can induce transient increases in testosterone, and anthropometric markers of adiposity correlate with testosterone concentrations.
Matthew R. Nelson, Robert K. Conlee and Allen C. Parcell
In Delayed Onset Muscle Soreness (DOMS), muscles become sore 24 to 48 hours after eccentric and unaccustomed activity. Fiber stiffness, due to decreased muscle glycogen, may predispose muscle to greater damage during eccentric exercise. This study sought to determine if inadequate carbohydrate intake following a protocol to decrease muscle glycogen would increase DOMS after 15 min of downhill running. Thirty-three male subjects (age, 18–35 years) were randomized into 3 groups for testing over a 7-day period. The depletion (DEP) group (n = 12) underwent a glycogen depletion protocol prior to a 15-min downhill run designed to induce DOMS. The repletion (FED) group (n = 10) underwent a glycogen depletion protocol followed by a carbohydrate repletion protocol (>80% CHO) prior to downhill running. The third (ECC) group (n = 11) performed only the downhill running protocol. Subjective muscle soreness, isometric force production, relaxed knee angle, and thigh circumference were measured pretreatment and on days 1, 2, 3, 4, and 6 post treatment. Subjective muscle soreness for all groups increased from 0 cm pretreatment to 3.05 ± 0.72 cm (on a 10-cm scale) on day 1 post treatment (p < .05). All groups were significantly different from baseline measurements until day 4 post treatment. Each group experienced a decline in isometric force from 281 ± 45 N pre-to 253 ± 13 N on day 1 post treatment (p < .05). The decrease in isometric force persisted in all groups for 4 days post treatment. Increases in thigh circumference and relaxed knee angle elevations in all 3 groups were statistically different (p < .05) from pretreatment until day 4. No differences were noted between groups for any of the parameters examined. In the current study, 15 min of downhill running is sufficient to cause DOMS with the associated functional and morphological changes; however, inadequate carbohydrate intake after a glycogen depleting exercise does not appear to exacerbate DOMS and the associated symptoms.
Kenneth W. Kambis and Sarah K. Pizzedaz
Creatine monohydrate (CrH2O) supplementation has been demonstrated to increase skeletal muscle power output in men. However, its effect upon women is not as clearly defined. This study investigated the effect of oral creatine supplementation upon muscle function, thigh circumference, and body weight in women. Twenty-two consenting college-age women were assigned to 1 of 2 groups matched for dietary and exercise habits, phase of menstrual cycle, and fat-free mass (FFM). After familiarization with testing procedures, pretrial measures of muscle function (5 repetitions 60 deg · s−1 and 50 repetitions 180 deg · s−1) were conducted during maximal voluntary concentric contraction of the preferred quadriceps muscle using an isokinetic dynamometer. Subjects then ingested 0.5 g · kg−1 FFM of either CrH2O or placebo (one fourth dosage 4 times daily) in a double-blind design for 5 days. Resistance exercise was prohibited. After the ingestion phase was completed, all measures were repeated at the same time of day as during pretrials. Statistical analysis revealed time to peak torque in quadriceps extension decreased from pre-test values of 255 ± 11 ms (mean ± SEM) to post-test values of 223 ± 3 ms; average power in extension increased from 103 ± 7 W pre-test to 112 ± 7 W post-test; and, during flexion, average power increased from 59 ± 5 W pre-test to 65 ± 5 W post-test in the creatine group as compared to controls (p ≤ .05). FFM, percent body fat, mid-quadriceps circumference, skinfold thickness of the measured thigh, and total body weight did not change for both groups between trials. We conclude that CrH2O improves muscle performance in women without significant gains in muscle volume or body weight.