Two force sensing resistor force transducers were utilized to measure the forces on the hand of seven skilled tennis players performing the tennis forehand drive. Repeatable gripping force patterns were recorded for the subjects given the experimental protocol used for the study. The magnitude of the peak postimpact force on the hand was highly variable, ranging from 4 to 309 N, and was found to be related to high-frequency vibrations of the racket. There was less variability in the magnitude of preimpact gripping forces, indicating that the subjects utilized a consistent gripping pattern in preparation for impact. The large within- and between-subject variability of postimpact forces warrant further study in order to establish the range of loadings in tennis play that may be related to overuse injuries.
Duane V. Knudson and Scott C. White
Scott C. White and David Winter
Repeat trials of a race walker were analyzed to ascertain the contribution to energy changes made by the lower limb muscles. A sagittal plane link segment model was used to calculate mechanical powers at the hip, knee and ankle. The ankle plantarflexors provided the major energy necessary to propel the body forward. Muscles about the hip contribute to a lesser extent via energy generation and transfer. At the knee, the muscles acted mainly as energy absorbers and did not contribute to forward propulsion. Mechanical powers calculated for the race walker were compared to other forms of locomotion. Patterns unique to the race walker were identified and discussed.
Scott C. White, Louise A. Gilchrist, and Kathryn A. Christina
Prescribing an appropriate adaptation period is an important consideration when using treadmills for locomotion studies. The present study investigated within-trial accommodation to running on a force measuring treadmill. Force measures were derived from vertical reaction force records of 16 runners; 8 were experienced in running on a treadmill. Three dependent measures, the peak impact force (F1), the loading rate of the impact force (LR), and the peak active force (F2) were tested for significant differences (p < 0.05) every 2 minutes of a continuous 20-min run using a two-factor ANOVA (group × time) with one repeated measure (time). Coefficients of variation (CV) for each dependent measure were tested for statistical significance in the same way. There were no significant differences in F1, LR, or F2 over any samples for the 20-min running trials. There were no significant changes in CV values for the duration of the run. The results from the present study suggest that after 30 seconds of treadmill running, there were no significant within-day accommodation effects on vertical force measures over a 20-min treadmill run. Variability between individuals in the consistency of force measures, however, could be a confounding factor. This lack of consistent response for individuals should be considered when exposing participants to experimental designs involving treadmill locomotion.
Vanessa R. Yingling, H. John Yack, and Scott C. White
This study investigated whether rearfoot motion at heel contact during running attenuates the magnitude of the impact force traveling through the body. Fifteen subjects completed running trials for two conditions:(a) running on a treadmill at a self-selected speed and a cadence of 160 steps/min and (b) running at the same speed and cadence but with rearfoot motion limited by a medial wedge inserted into the subject's shoe. A paired t test was used to test for differences between conditions in the peak accelerations of each accelerometer and the time to peak of the tibia acceleration. The predominant impact frequency and amplitude of the frequency peak were also tested for significant differences. No significant difference was found in the variables compared between the two conditions. The results demonstrated that restriction of rearfoot motion using a medial wedge during the initial 15% of the stance phase has no effect on the characteristics of the impulse wave at the tibia.
Brian J. O'Connor, H. John Yack, and Scott C. White
A strategy is presented for temporally aligning ground reaction force and kinematic data. Alignment of these data requires marking both the force and video records at a common event. The strategy uses the information content of the video signal, which is A/D converted along with the ground reaction force analog signals, to accomplish this alignment in time. The vertical blanking pulses in the video signal, which define the start of each video field, can be readily identified, provided the correct A/D sampling rate is selected. Knowledge of the position of these vertical blanking pulses relative to the synchronization pulse makes it possible to precisely align the video and analog data in time. Choosing an A/D sampling rate of 598 Hz would enable video and analog data to be synchronized to within 1/1,196 s. Minimizing temporal alignment error results in greater accuracy and .reliability in calculations used to determine joint kinetics.