Paper # 75: Earlier Lower Extremity Neuromuscular Activation Timing, Ground Reaction Force Timing, and Kick Quickness After Progressive Resistance, Whole Body, Long‐Axis Rotational Training (2011)

Optimized lower extremity neuromuscular activation and peak ground reaction force timing can help improve athletic performance and decrease injury risk. This prospective, randomized, controlled study evaluated the efficacy of short-term progressive resistance, whole body, long-axis rotational exercise training for improving lower extremity neuromuscular activation, peak ground reaction force timing, and kick quickness of healthy subjects. Thirty-six (18 men, 18 women) healthy, recreational athletes (age = 24.1 ± 5 yrs, height = 175.7 ± 10 cm, weight = 72.9 ± 11 kg) participated in this pre-test, post-test design study. Subjects were randomly assigned to groups with an equal number of men and women. The median 2000 IKDC Self-Reported Activity Level was 3 (well-trained and frequently sporting) for both groups. Subjects ranged from level 2 (sporting sometimes) to level 4 (highly competitive). Over a four-week period the training group (Group 1) performed nine, 20 min exercise sessions consisting of seven sets on a Ground Force 360 Device. The control group (Group 2) did not use the test device. Both groups continued regular athletic activities (soccer, basketball, tennis, swimming, volleyball, running) without increasing frequency, intensity, or total volume. Surface EMG electrodes were applied over the gluteus maximus, gluteus medius, vastus medialis, rectus femoris, vastus lateralis, medial hamstrings, biceps femoris and gastrocnemius of the left lower extremity. A retro-reflective marker demarcated the fifth metatarsal head of the left foot. Time-synchronized EMG (1,000 Hz), two-dimensional sagittal plane kinematic (60 Hz), and peak resultant ground reaction force (1,000 Hz) data were collected as subjects, after assuming an athletic ready standing position, responded to a randomly timed audio cue (range = 6535-57800 msec) by kicking a traffic cone placed 40 cm in front of the anterior force platform edge as quickly as possible with their left foot. Groups did not differ for audio cue timing (mean ± standard deviation)(Group 1 = 14844 ± 3916 msec; Group 2 = 14704 ± 2261 msec)(P = 0.92). After rectification, the root mean square of the EMG signal was determined using a 50 msec moving window function. EMG signal activation timing (+/ 10 mV) was measured from cue onset using a manual cursor. Independent sample T-Tests with Bonferroni adjustments for multiple comparisons were used to compare group mean change differences (P = 0.05 / 11 < 0.0045). Group 1 displayed more improved gluteus maximus (−75.7 ± 94 msec vs. 7.0 ± 54 msec, P = 0.004), gluteus medius (−51.4 ± 68 msec vs. 24.5 ± 43 msec, P = 0.001), rectus femoris (−61.5 ± 77 msec vs. 19.6 ± 68 msec, P = 0.003), medial hamstrings (−47.4 ± 68 msec vs. 11.6 ± 45 msec, P = 0.004), and biceps femoris (−45.2 ± 52 msec vs. 18.7 ± 56 msec, P = 0.002) neuromuscular activation timing compared to Group 2. Significant differences were not observed for vastus medialis, vastus lateralis, or gastrocnemius. Group 1 had more improved kick quickness (−30.6 ± 39 msec vs. 8.8 ± 44.7 msec, P = 0.004) and earlier peak resultant ground reaction force timing (−31.2 ± 39.1 msec vs. −1.1 ± 26 msec, P = 0.004) compared to Group 2. Significant differences were not observed for peak resultant ground reaction force magnitude. Earlier gluteus maximus, gluteus medius, rectus femoris, medial hamstrings, and biceps femoris neuromuscular activation timing, earlier peak resultant ground reaction force timing, and quicker kicking speed in the training group suggests that test device use may improve the lower extremity neuromuscular activation needed for athletic performance and knee injury prevention.