Acute lower extremity running kinematics after a hamstring stretch.

CONTEXT: Limited passive hamstring flexibility might affect kinematics, performance, and injury risk during running. Preactivity static straight-leg raise stretching often is used to gain passive hamstring flexibility. OBJECTIVE: To investigate the acute effects of a single session of passive hamstring stretching on pelvic, hip, and knee kinematics during the swing phase of running. DESIGN: Randomized controlled clinical trial. SETTING: Biomechanics research laboratory. PATIENTS OR OTHER PARTICIPANTS: Thirty-four male (age = 21.2 ± 1.4 years) and female (age = 21.3 ± 2.0 years) recreational athletes. INTERVENTION(S): Participants performed treadmill running pretests and posttests at 70% of their age-predicted maximum heart rate. Pelvis, hip, and knee joint angles during the swing phase of 5 consecutive gait cycles were collected using a motion analysis system. Right and left hamstrings of the intervention group participants were passively stretched 3 times for 30 seconds in random order immediately after the pretest. Control group participants performed no stretching or movement between running sessions. MAIN OUTCOME MEASURE(S): Six 2-way analyses of variance to determine joint angle differences between groups at maximum hip flexion and maximum knee extension with an α level of .008. RESULTS: Flexibility increased between pretest and posttest in all participants (F(1,30) = 80.61, P < .001). Anterior pelvic tilt (F(1,30) = 0.73, P = .40), hip flexion (F(1,30) = 2.44, P = .13), and knee extension (F(1,30) = 0.06, P = .80) at maximum hip flexion were similar between groups throughout testing. Anterior pelvic tilt (F(1,30) = 0.69, P = .41), hip flexion (F(1,30) = 0.23, P = .64), and knee extension (F(1,30) = 3.38, P = .62) at maximum knee extension were similar between groups throughout testing. Men demonstrated greater anterior pelvic tilt than women at maximum knee extension (F(1,30) = 13.62, P = .001). CONCLUSIONS: A single session of 3 straight-leg raise hamstring stretches did not change pelvis, hip, or knee running kinematics.

Target heights alter the energetics of drop jumps when drop height is held constant.

Plyometrics are a popular form of training the stretch-shortening cycle in competitive athletes and recreational athletes. One method of controlling intensity is to vary the dropping height during the training session. It may be possible to alter the intensity by creating a target height to jump over when holding the dropping height constant. Fifteen college recreational athletes performed 15 trials of 60-cm depth jumps over 3 different target heights (40, 60, and 80 cm). One-way repeated measures analysis of variance was used to identify significant differences in kinematic and kinetic variables for both the concentric and eccentric phases. There were no significant differences in eccentric work found between the 3 conditions. Significant differences were found in the total work performed during the concentric portion of the jumps between the 40- and 60-cm trials but not between the 60- and 80-cm trials. These results were found to be different at each joint of the lower extremity as compared with past research. Power analysis showed no significant differences between target heights, which may suggest that higher target heights may not be necessary to achieve the same ground contact parameters. Overall analysis of the variables suggests that 60 cm is an adequate target height when dropping from 60 cm.

Muscle activation following sudden ankle inversion during standing and walking.

Dynamic response characteristics of ankle musculature following sudden ankle inversion have traditionally been tested in a static, standing position. However, this model does not take into consideration muscle activity and loading characteristics associated with active gait. This study compared muscle reaction times and amplitudes from sudden ankle inversion during standing (standing group) and walking (walking group) using one of two similar devices for each of these conditions. Surface EMG was collected from the peroneus longus (PL), brevis (PB), and tibialis anterior (TA) of the dominant leg from 25 subjects (age 20 +/- 1 years, height 174.0 +/- 10.2 cm, mass 74.3 +/- 12.9 kg) for each condition (walking and standing). Time to total inversion ROM (28 degrees ) was greater in the walking group (114.9 +/- 15.0 ms) than the standing group (65.6 +/- 17.8 ms, P < 0.05), whereas reaction time was less in the peroneals in the walking group (PL 56.9 +/- 8.4 ms, PB 60.1 +/- 10.6 ms, TA 65.0 +/- 14.9 ms) compared to the standing group (PL 74.3 +/- 8.5 ms, PB 73.5 +/- 8.2 ms, TA 73.3 +/- 8.3, P < 0.05). Additionally, Peak normalized EMG (% MVIC) for the walking condition (PL 367 +/- 254, PB 405 +/- 359, TA 84 +/- 39) exceeded that of the standing condition (PL 310 +/- 239, PB 328 +/- 215, TA 76 +/- 39, P < 0.05), and average normalized EMG (% MVIC) was greater in the peroneals for the walking condition (PL 233 +/- 171, PB 280 +/- 255) than the standing condition (PL 164 +/- 131, PB 193 +/- 137, P < 0.05). The differences noted between the conditions provide evidence that a dynamic response to ankle injury mechanisms is much different in a walking model compared to a traditional standing model. A walking model may be a more functional approach for evaluating dynamic response characteristics of ankle musculature due to sudden ankle inversion.