Interrelationships among thigh muscle co-contraction, quadriceps muscle strength and the aerobic demand of walking in children with cerebral palsy.

The purpose of this study was to quantify interrelationships among thigh muscle co-contraction, quadriceps muscle strength, and the aerobic demand of walking in 13 children with spastic hemiplegic cerebral palsy (CP). During Session 1, subjects were familiarized with testing procedures, given five minutes of treadmill walking practice, and completed quadriceps muscle strength testing. In Session 2, subjects performed three 5-min walking bouts on the treadmill at 0.67 m x s(-1) to further accommodate to treadmill ambulation. During Session 3, resting VO2 was measured and subjects walked at 0.67, 0.89, and 1.12 m x s(-1) for five minutes while oxygen uptake (VO2) and thigh muscle co-contraction data were collected. Results demonstrated that no significant relationship existed between net VO2 and measures of thigh muscle co-contraction or quadriceps muscle strength. In addition, thigh muscle co-contraction was not shown to be associated with quadriceps muscle strength. Collectively, thigh muscle co-contraction and quadriceps muscle strength explained 13. 5%, 6.2%, and 2.2% of the variance in VO2 at 0.67, 0.89, and 1.12 m x s(-1), respectively. Viewed in concert, these results suggest that the walking energy expenditure of children with spastic hemiplegic CP is not influenced by the level of thigh muscle co-contraction or quadriceps muscle strength.

Electromechanical delay in isometric actions initiated from nonresting levels.

PURPOSE: The purpose of this study was to determine whether electromechanical delay (EMD) was associated exclusively with the onset of tension from a resting state and whether EMD remained constant across different rates of force development. METHODS: Twenty-four subjects (23.9 +/- 5.4 yr, 171.7 +/- 7.3 cm, 72.9 +/- 12.8 kg) performed isometric elbow flexion trials in the transverse plane by using the dominant arm during which isometric force data and surface EMG activity were collected. Subjects completed three trials to establish a maximal force (MF) reference. Subjects then completed trials in which pulse forces of varying magnitudes were elicited at a frequency of 1 Hz from different baseline intensities. All forces were expressed relative to MF. Three trials of the following conditions (baseline-pulse) were performed in random order: 0-25%, 25-50%, 50-75%, 0-50%, and 0-75%. EMG and force data were collected for 10 pulse cycles during these trials. EMD was defined as the temporal shift that maximized a normalized cross-correlation function. RESULTS: EMD for a 25% pulse force developed from rest (83.5 +/- 12.9 ms) was significantly longer than that developed from 25% (66.3 +/- 11.5 ms) or 50% (60.6 +/- 16.6 ms) baselines. EMD values were not different when force was developed from 25% and 50% baselines. EMD associated with a 25% pulse force from rest was significantly longer than 50% (70.3 +/- 10.0 ms) and 75% (68.9 +/- 8.7 ms) pulse forces from rest. EMD for 50% and 75% pulse forces from rest were not statistically different. CONCLUSION: It was concluded that EMD is present during exertions initiated from both resting and nonresting states but is reduced when exertions are initiated from non-resting states and with higher rates of force development.

Endpoint error in smoothing and differentiating raw kinematic data: an evaluation of four popular methods.

'Endpoint error' describes the erratic behavior at the beginning and end of the computed acceleration data which is commonly observed after smoothing and differentiating raw displacement data. To evaluate endpoint error produced by four popular smoothing and differentiating techniques, Lanshammar's (1982, J. Biomechanics 15, 99-105) modification of the Pezzack et al. (1977, J. Biomechanics, 10, 377-382) raw angular displacement data set was truncated at three different locations corresponding to the major peaks in the criterion acceleration curve. Also, for each data subset, three padding conditions were applied. Each data subset was smoothed and differentiated using the Butterworth digital filter, cubic spline, quintic spline, and Fourier series to obtain acceleration values. RMS residual errors were calculated between the computed and criterion accelerations in the endpoint regions. Although no method completely eliminated endpoint error, the results demonstrated clear superiority of the quintic spline over the other three methods in producing accurate acceleration values close to the endpoints of the modified Pezzack et al. (1977) data set. In fact, the quintic spline performed best with non-padded data (cumulative error = 48.0 rad s-2). Conversely, when applied to non-padded data, the Butterworth digital filter produced wildly deviating values beginning more than the 10 points from the terminal data point (cumulative error = 226.6 rad s-2). Each of the four methods performed better when applied to data subsets padded by linear extrapolation (average cumulative error = 68.8 rad s-2) than when applied to analogous subsets padded by reflection (average cumulative error = 86.1 rad s-2).

Effects of acute inhalation of albuterol on submaximal and maximal VO2 and blood lactate.

The acute effects of inhaled albuterol, a selective beta-2 adrenergic agonist, on measures of endurance cycling performance and pulmonary function were assessed in 21 competitive road cyclists. A 5 step methacholine challenge revealed all cyclists to be non-asthmatic. Albuterol (A) total dose 360 micrograms or a saline placebo (P) was administered by inhaler, in 4 metered doses of 90 micrograms each, 15 minutes before cycle ergometry exercise. Heart rate, whole blood lactate, perceived exertion and VO2 were determined at the submaximal workloads of 150, 200, 225, 250, 275, 300 watts and at max. Pulmonary function tests determining forced vital capacity, forced expiratory volume during the first second of expiration, forced mid-expiratory flow and maximal voluntary ventilation were performed prior to and 10 minutes after inhalation; and 5, 10 and 15 minutes after termination of the exercise protocol. Heart rate was significantly greater during the A compared to the P treatment at 200 (150.8 +/- 2.5 vs 146.7 +/- 2.8 beats per minute), 225 (159.7 +/- 2.4 vs 154.6 +/- 2.7 beats per minute) and 250 watts (166.9 +/- 2.4 vs 164.4 +/- 2.6 beats per minute). Whole blood lactate was significantly greater during the A compared to the P treatment at 275 watts (4.7 +/- 0.3 vs 4.2 +/- 0.4 mmol.l-1). No other significant differences were found between the 2 treatments at any time point. These data indicate that the acute effect of albuterol inhalation at twice the recommended dosage has no positive effect on endurance performance measures or pulmonary function in athletes who are not asthmatic.