The effects of lower extremity muscle activation and passive range of motion on single leg squat performance.

Knee valgus is a potential risk factor for lower extremity (LE) injuries. Clinical movement screenings and passive range of motion (PROM) measurements may help identify neuromuscular patterns, which contribute to knee valgus. The purpose of this study was to compare LE muscle activation and PROM between subjects who display visual medial knee displacement (MKD) during a single leg squat (SLS) and those who do not. We hypothesized that muscular activation and PROM would differ between the groups. Forty physically active adults (20 controls, 20 MKDs) participated in this study. Subjects completed 10 LE PROM assessments and performed 5 SLS trials while electromyography (EMG) data were collected from 8 LE muscles. Three separate multivariate analysis of variance were used to identify group differences in EMG data, muscle coactivation, and PROM. Results during the SLS indicated hip coactivation ratios revealed smaller gluteus medius to hip adductor (GMed:Hip Add) (p = 0.028) and gluteus maximus to hip adductor (GMax:Hip Add) coactivation ratios (p = 0.007) compared with the control group. Also, the MKD group displayed significantly less passive ankle dorsiflexion with the knee extended (p = 0.047) and flexed (p = 0.034), and greater talar glide motion (p = 0.012). The findings of this study indicate that MKD during a SLS seems to be influenced by decreased coactivation of the gluteal to the hip adductor muscles and restricted dorsiflexion. Therefore, conditioning, rehabilitation, and injury prevention programs should focus on decreasing hip adductor activity, increasing hip abductor and external rotator activity, and increasing ankle dorsiflexion in hopes to decrease the incidence of these injuries.

Muscle activation during side-step cutting maneuvers in male and female soccer athletes.

CONTEXT: Female soccer athletes are at greater risk of anterior cruciate ligament (ACL) injury than males. Sex differences in muscle activation may contribute to the increased incidence of ACL injuries in female soccer athletes. OBJECTIVE: To examine sex differences in lower extremity muscle activation between male and female soccer athletes at the National Collegiate Athletic Association Division I level during 2 side-step cutting maneuvers. DESIGN: Cross-sectional with 1 between-subjects factor (sex) and 2 within-subjects factors (cutting task and phase of contact). SETTING: Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty males (age = 19.4 +/- 1.4 years, height = 176.5 +/- 5.5 cm, mass = 74.6 +/- 6.0 kg) and 20 females (age = 19.8 +/- 1.1 years, height = 165.7 +/- 4.3 cm, mass = 62.2 +/- 7.2 kg). INTERVENTION(S): In a single testing session, participants performed the running-approach side-step cut and the box-jump side-step cut tasks. MAIN OUTCOME MEASURE(S): Surface electromyographic activity of the rectus femoris, vastus lateralis, medial hamstrings, lateral hamstrings, gluteus medius, and gluteus maximus was recorded for each subject. Separate mixed-model, repeated-measures analysis of variance tests were used to compare the dependent variables across sex during the preparatory and loading contact phases of each cutting task. RESULTS: Females displayed greater vastus lateralis activity and quadriceps to hamstrings coactivation ratios during the preparatory and loading phases, as well as greater gluteus medius activation during the preparatory phase only. No significant differences were noted between the sexes for muscle activation in the other muscles analyzed during each task. CONCLUSIONS: The quadriceps-dominant muscle activation pattern observed in recreationally active females is also present in female soccer athletes at the Division I level when compared with similarly trained male soccer athletes. The relationship between increased quadriceps activation and greater incidence of noncontact ACL injury in female soccer athletes versus males requires further study.

Functional balance training, with or without exercise sandals, for subjects with stable or unstable ankles.

CONTEXT: Improving postural stability through balance training may prevent ankle sprains. Exercise Sandals may increase the demands placed on ankle muscles during rehabilitation, which could improve postural stability. OBJECTIVE: To examine the effects of functional balance training, with and without the use of Exercise Sandals, on postural stability in subjects with stable or unstable ankles. DESIGN: Prospective, nonrandomized clinical trial. SETTING: Sports medicine research laboratory. PATIENTS OR OTHER PARTICIPANTS: Sixteen subjects with functional ankle instability and 16 subjects with no history of ankle sprains. INTERVENTION(S): Subjects were assigned to an Exercise Sandal functional balance training group or a shoe functional balance training group. Subjects trained 3 times per week for 8 weeks and then performed a single-limb stance posttest. MAIN OUTCOME MEASURE(S): Subjects were required to remain as motionless as possible during a single-limb stance pretest. Anterior-posterior and medial-lateral center-of-pressure excursions were measured. RESULTS: Exercise Sandal balance training improved anterior-posterior postural stability in both ankle groups ( P < .05). Both training interventions improved medial-lateral postural stability in stable and unstable ankles ( P < .05). CONCLUSIONS: Postural stability improved after subjects performed functional balance training programs, both with and without Exercise Sandals. Training with Exercise Sandals might not be any more effective in improving postural stability than performing functional balance training without Exercise Sandals. However, Exercise Sandals did not impair postural stability and, consequently, might serve as an alternative therapy to improve postural stability.

Exercise Sandals Increase Lower Extremity Electromyographic Activity During Functional Activities.

OBJECTIVE: Anecdotal evidence suggests that use of Exercise Sandals results in a number of positive clinical outcomes. However, little research has been conducted to determine their efficacy objectively. Our purposes were to determine the effect of Exercise Sandals on lower leg electromyography (EMG) during activities in the Exercise Sandals and to compare EMG associated with Exercise Sandals with traditional lower extremity rehabilitation exercises. DESIGN AND SETTING: Two within-subjects, repeated-measures designs were used to identify differences in lower extremity EMG: (1) between activities with and without Exercise Sandals and (2) between Exercise Sandals activities and traditional rehabilitation activities. All data were collected in the Sports Medicine Research Laboratory. SUBJECTS: Eighteen subjects involved in rehabilitation using Exercise Sandals for at least 2 weeks within the year before data collection. MEASUREMENTS: Mean EMG amplitudes from the tibialis anterior, peroneus longus, soleus, and lateral gastrocnemius muscles were measured during single-leg stance, side stepping, and "high knees," all performed with and without the Exercise Sandals, as well as single-leg stance on a foam surface and T-band kicks in the sagittal and frontal planes. RESULTS: Exercise Sandals increased lower leg EMG activity, particularly in the ankle invertors and evertors. Also, activities involving the Exercise Sandals resulted in EMG activity similar to or exceeding that associated with traditional ankle-rehabilitation exercises. CONCLUSIONS: These results, coupled with the fact that Exercise Sandals are used in a functional closed kinetic chain manner, suggest that they are an effective means of increasing lower extremity muscle activity.