THE INFLUENCE OF HEEL HEIGHT ON MUSCLE ELECTROMYOGRAPHY OF THE LOWER EXTREMITY DURING LANDING TASKS IN RECREATIONALLY ACTIVE FEMALES: A WITHIN SUBJECTS RANDOMIZED TRIAL.

BACKGROUND: An increased risk of ACL injury has been shown in female athletes who land from jumping maneuvers with knee angles close to extension and in those who demonstrate a hamstring-to-quadriceps muscle recruitment imbalance. HYPOTHESIS/PURPOSE: The purpose of this study was to determine if added heel lift height would alter electromyography (EMG) magnitude and timing of the quadriceps (vastus medialis, vastus lateralis), hamstrings (semitendinosus, biceps femoris) and gastroc (medial gastroc, lateral gastroc) musculature during forward jump and drop-rebound jump landing tasks in females. The authors hypothesized increased heel lift height would promote recruitment of the hamstring and gastrocnemius muscles and increase the time to peak muscle activity in the quadriceps muscles. STUDY DESIGN: Prospective randomized trial. METHODS: 60 recreationally active females participated. Participants performed five repetitions of forward jump and drop-rebound jump landing tasks while wearing different heel lifts heights (0, 12, 18, 24 mm) placed on the under-side of an athletic shoe. Task order and heel lift height were randomized. Dependent measures were average magnitude of muscle recruitment (AMR), peak magnitude of muscle recruitment (PMR), and time to reach PMR for six lower extremity muscle groups as measured by surface EMG. RESULTS: Repeated measures ANOVAs were used to determine the influence of heel lift height on the dependent measures. There were no signficant differences in the AMR, PMR, or time to reach PMR with the four different heel heights during the landing maneuvers, with one exception. A significant difference was found in the time to achieve PMR in the semitendinosis muscle during a forward jump landing (p = .024). Post hoc analysis found significant differences with both the 18mm and 24mm heel lift height compared to 0mm. CONCLUSIONS: Utilization of larger heel lifts (18mm and 24mm) to influence landing biomechanics may be of potential benefit; however, only when performing forward jump landing tasks. Further investigation into the protective effects of a quicker onset of semitendinosis peak magnitude is warranted. LEVEL OF EVIDENCE: 2.

The influence of heel height on vertical ground reaction force during landing tasks in recreationally active and athletic collegiate females.

PURPOSE: To determine if heel height alters vertical ground reaction forces (vGRF) when landing from a forward hop or drop landing. BACKGROUND: Increased vGRF during landing are theorized to increase ACL injury risk in female athletes. METHODS: Fifty collegiate females performed two single-limb landing tasks while wearing heel lifts of three different sizes (0, 12 & 24 mm) attached to the bottom of a athletic shoe. Using a force plate, peak vGRF at landing was examined. Repeated measures ANOVAs were used to determine the influence of heel height on the dependent measures. RESULTS: Forward hop task- Peak vGRF (normalized for body mass) with 0 mm, 12 mm, and 24 mm lifts were 2.613±0.498, 2.616±0.497 and 2.495±0.518% BW, respectively. Significant differences were noted between 0 and 24 mm lift (p<.001) and 12 and 24 mm lifts (p=.004), but not between the 0 and 12 mm conditions (p=.927). Jump-landing task- No significant differences were found in peak vGRF (p=.192) between any of the heel lift conditions. CONCLUSIONS: The addition of a 24 mm heel lift to the bottom of a sneaker significantly alters peak vGRF upon landing from a unilateral forward hop but not from a jumping maneuver.

The influence of heel height on sagittal plane knee kinematics during landing tasks in recreationally active and athletic collegiate females.

PURPOSE: To determine if heel height alters sagittal plane knee kinematics when landing from a forward hop or drop landing. BACKGROUND: Knee angles close to extension during landing are theorized to increase ACL injury risk in female athletes. METHODS: Fifty collegiate females performed two single-limb landing tasks while wearing heel lifts of three different sizes (0, 12 & 24 mm) attached to the bottom of a sneaker. Using an electrogoniometer, sagittal plane kinematics (initial contact [KA(IC)], peak flexion [KA(Peak)], and rate of excursion [RE]) were examined. Repeated measures ANOVAs were used to determine the influence of heel height on the dependent measures. RESULTS: Forward hop task- KA(IC) with 0 mm, 12 mm, and 24 mm lifts were 8.88±6.5, 9.38±5.8 and 11.28±7.0, respectively. Significant differences were noted between 0 and 24 mm lift (p<.001) and 12 and 24 mm lifts (p=.003), but not between the 0 and 12 mm conditions (p=.423). KA(Peak) with 0 mm, 12 mm, and 24 mm lifts were 47.08±10.9, 48.18±10.3 and 48.88±9.7, respectively. A significant difference was noted between 0 and 24 mm lift (p=.004), but not between the 0 and 12 mm or 12 and 24 mm conditions (p=.071 and p=.282, respectively). The RE decreased significantly from 2128/sec±52 with the 12 mm lift to 1958/sec±55 with the 24 mm lift (p=.004). RE did not differ from 0 to 12 or 0 to 24 mm lift conditions (p=.351 and p=.086, respectively). Jump-landing task- No significant differences were found in KA(IC) (p=.531), KA(Peak) (p=.741), or the RE (p=.190) between any of the heel lift conditions. CONCLUSIONS: The addition of a 24 mm heel lift to the bottom of a sneaker significantly alters sagittal plane knee kinematics upon landing from a unilateral forward hop but not from a drop jump.

Muscle response times between shoe and no-shoe conditions following a weight-bearing rotary perturbation are similar in females.

The purpose of this study was to compare the muscle response times (MRTs) of select lower extremity muscles following a weight bearing rotary perturbation in single-leg stance with and without shoes. Ten recreationally active females volunteered for this study. Each subject received a rotary perturbation in single-leg stance under two conditions: with shoes and without shoes. The outcomes measured were response times of the medial and lateral quadriceps, hamstrings and gastrocnemius. The results demonstrated that significant differences in MRTs were not apparent for either the medial or lateral perturbation between conditions. While a main effect for muscle was evident for both medial and lateral perturbations, a muscle by shoe interaction was not present for either the medial or lateral perturbation. Our findings suggest that wearing shoes does not alter MRTs during single-limb rotary perturbations. These data indicate that lower extremity perturbation device testing may be done with or without shoes and comparisons between works are permissible as response times are unaffected.