This study compared impact forces and loading rates in a high and low impact aerobic dance movement. Five subjects each performed five trials of the low impact front knee lift (LFKL) and five trials of the high impact front knee lift (HFKL). The data were recorded using an AMTI force plate at 1,000 Hz. A repeated-measures ANOVA was used to test for differences in selected variables for the LFKL and HFKL. Peak impact force was significantly lower in the LFKL than the HFKL, mean 0.98 BW and 1.98 BW, respectively. Mean loading rate was significantly lower in the LFKL (14.38 BW/s) than the HFKL (42.55 BW/s). Mean impact impulse during the first 50 ms of impact was significantly lower in the LFKL (0.0131 BW•s) than the HFKL (0.0295 BW•s). Based upon these differences in external ground reaction forces, it appears that low impact front knee lifts impose a significantly lower load than high impact front knee lifts.
Mark D. Ricard and Steve Veatch
Mark D. Ricard and Steve Veatch
Aerobic dance movement sequences are similar to running in repetitive frequency. The purpose of this study was to compare ground reaction force variables in aerobic dance and running. Five female subjects performed 10 trials of five running speeds (2.4–4.0 ± 0.4 m/s) and five heights (0–8 ± 0.2 cm) of front knee lift aerobic dance steps on an AMTI force plate (1000 Hz). First peak impact force, peak loading rate, high-frequency impulse, and 50-ms impulse increased with increased running speed and jumping height. Time to first peak impact force decreased as running speed and jumping height increased. Although first peak impact forces resulting from airborne aerobic dance movements (1.96–2.62 BW) were greater than first peak impact forces in running (1.30–2.01 BW), running compared to aerobic dance resulted in shorter time to first peak impact force and higher values for loading rate, high-frequency impulse, and 50-ms impulse. When compared to aerobic dance, running exhibits smaller peak vertical forces but higher loading rates and vertical impulses.
KyungMo Han and Mark D. Ricard
Several researchers have suggested that improving evertor strength and peroneus longus reaction time may help alleviate the symptoms of chronic ankle instability and reduce the rate of recurrent ankle sprains.
To determine the effectiveness of a 4-wk elastic-resistance exercise-training program on ankle-evertor strength and peroneus longus latency in subjects with and without a history of ankle sprains (HAS).
Randomized controlled clinical trial.
40 subjects (20 male, 20 female; 20 HAS, 20 healthy). Ten subjects (5 male and 5 female) from each of the HAS and healthy groups were randomly assigned to exercise or control groups.
4-directional elastic-resistance exercise training 2 times/wk for 4 wk.
Main Outcome Measures:
Ankle-evertor strength and peroneal muscle latency after sudden inversion were measured before training, after 4 wk of training, and 4 wk posttraining.
Four weeks of elastic-resistance exercise training did not elicit significant changes in 1-repetition-maximum ankle-evertor strength between the exercise and control groups (P = .262), HAS and healthy groups (P = .329), or males and females (P = .927). Elastic-resistance exercise training did not elicit significant changes in peroneus longus muscle latency between the exercise and control groups (P = .102), HAS and healthy groups (P = .996), or males and females (P = .947).
The 4-wk elastic-resistance exercise training had no effect on ankle-evertor strength and reflex latency of the peroneus longus after unexpected ankle inversion.
Joseph Hamill, Mark D. Ricard and Dennis M. Golden
A study was undertaken to investigate the changes in total body angular momentum about a transverse axis through the center of mass that occurred as the rotational requirement in the four categories of nontwisting platform dives was increased. Three skilled subjects were filmed performing dives in the pike position, with increases in rotation in each of the four categories. Angular momentum was calculated from the initiation of the dive until the diver reached the peak of his trajectory after takeoff. In all categories of dives, the constant, flight phase total body angular momentum increased as a function of rotational requirement. Increases in the angular momentum at takeoff due to increases in the rotational requirement ranged from a factor of 3.61 times in the forward category of dives to 1.52 times in the inward category. It was found that the remote contribution of angular momentum contributed from 81 to 89% of the total body angular momentum. The trunk accounted for 80 to 90% of the local contribution. In all categories of dives except the forward 1/2 pike somersault, the remote percent contribution of the arms was the largest of all segments, ranging from 38 to 74% of the total angular momentum.
Mack D Rubley, Jody B Brucker, Kenneth L Knight, Mark D Ricard and David O Draper
To determine the retention of flexibility 25 days after 5 days of three 30-second stretches.
A 2 × 4 repeated-measures factorial. Treatment and time were independent variables. The dependent variable was flexibility as measured by a sit-and-reach box.
33 college students were tested before and after stretching for 5 consecutive days and without stretching on days 8 and 30. Control subjects were prone for 15 minutes; stretch subjects received 15 min of diathermy or sham diathermy and then performed three 30-second standing right-hamstring stretches.
Flexibility was greater on days 5, 8, and 30 than day 1, but days 5, 8, and 30 were not different from each other.
Gains in flexibility are retained for at least 3 weeks after a stretching program. It also appears that 2 sets of 3 repetitions of a sit-and-reach test is sufficient stimulus to induce long-term flexibility gains.