Kellie C. Huxel

RELATIONSHIP BETWEEN CORE STABILITY, FUNCTIONAL MOVEMENT, AND PERFORMANCE

Okada, T, Huxel, KC, and Nesser, TW. Relationship between core stability, functional movement, and performance. J Strength Cond Res 25(1): 252-261, 2011-The purpose of this study was to determine the relationship between core stability, functional movement, and performance. Twenty-eight healthy individuals (age = 24.4 ± 3.9 yr, height = 168.8 ± 12.5 cm, mass = 70.2 ± 14.9 kg) performed several tests in 3 categories: core stability (flexion [FLEX], extension [EXT], right and left lateral [LATr/LATl]), functional movement screen (FMS) (deep squat [DS], trunk-stability push-up [PU], right and left hurdle step [HSr/HSl], in-line lunge [ILLr/ILLl], shoulder mobility [SMr/SMl], active straight leg raise [ASLRr/ASLRl], and rotary stability [RSr/RSl]), and performance tests (backward medicine ball throw [BOMB], T-run [TR], and single leg squat [SLS]). Statistical significance was set at p ≤ 0.05. There were significant correlations between SLS and FLEX (r = 0.500), LATr (r = 0.495), and LATl (r = 0.498). The TR correlated significantly with both LATr (r = 0.383) and LATl (r = 0.448). Of the FMS, BOMB was significantly correlated with HSr (r = 0.415), SMr (r = 0.388), PU (r = 0.407), and RSr (r = 0.391). The TR was significantly related with HSr (r = 0.518), ILLl (r = 0.462) and SMr (r = 0.392). The SLS only correlated significantly with SMr (r = 0.446). There were no significant correlations between core stability and FMS. Moderate to weak correlations identified suggest core stability and FMS are not strong predictors of performance. In addition, existent assessments do not satisfactorily confirm the importance of core stability on functional movement. Despite the emphasis fitness professionals have placed on functional movement and core training for increased performance, our results suggest otherwise. Although training for core and functional movement are important to include in a fitness program, especially for injury prevention, they should not be the primary emphasis of any training program.

The Relationship Between Core Stability and Performance in Division I Football Players

Nesser, TW, Huxel, KC, Tincher, JL, and Okado, T. The relationship between core stability and performance in Division I football players. J Strength Cond Res 22(6):1750-1754, 2008-The purpose of this study was to identify relationships between core stability and various strength and power variables in strength and power athletes. National Collegiate Athletic Association Division I football players (height 184.0 ± 7.1 cm, weight 100.5 ± 22.4 kg) completed strength and performance testing before off-season conditioning. Subjects were tested on three strength variables (one-repetition maximum [1RM] bench press, 1RM squat, and 1RM power clean), four performance variables (countermovement vertical jump [CMJ], 20- and 40-yd sprints, and a 10-yd shuttle run), and core stability (back extension, trunk flexion, and left and right bridge). Significant correlations were identified between total core strength and 20-yd sprint (r = −0.594), 40-yd sprint (r = −0.604), shuttle run (r = −0.551), CMJ (r = 0.591), power clean/body weight (BW) (r = 0.622), 1RM squat (r = −0.470), bench press/BW (r = 0.369), and combined 1RM/BW (r = 0.447); trunk flexion and 20-yd sprint (r = −0.485), 40-yd sprint (r = −0.479), shuttle run (r = −0.443), CMJ (r = 0.436), power clean/BW (r = 0.396), and 1RM squat (r = −0.416); back extension and CMJ (r = 0.536), and power clean/BW (r = 0.449); right bridge and 20-yd sprint r = −0.410) and 40-yd sprint (r = −0.435), CMJ (r = 0.403), power clean/BW (r = 0.519) and bench press/BW (r = 0.372) and combined 1RM/BW (r = 0.406); and left bridge and 20-yd sprint (r = −0.376) and 40-yd sprint (r = −0.397), shuttle run (r = −0.374), and power clean/BW (r = 0.460). The results of this study suggest that core stability is moderately related to strength and performance. Thus, increases in core strength are not going to contribute significantly to strength and power and should not be the focus of strength and conditioning.

Glenohumeral rotation and scapular position adaptations after a single high school female sports season.

CONTEXT Anterior instability and impingement are common in overhead athletes and have been associated with decreases in internal rotation (IR) and increases in external rotation (ER) motion. However, the chronology and the effect of different female sports on these conditions have yet to be determined. OBJECTIVE To measure glenohumeral IR and ER rotation, total range of motion, and scapular position in female overhead athletes over a single competitive season. DESIGN Multiple group pretest-posttest study. SETTING High school. PATIENTS OR OTHER PARTICIPANTS Thirty-six female overhead athletes (age = 15.29 +/- 1.18 years, height = 164.16 +/- 7.14 cm, mass = 58.24 +/- 9.54 kg) with no history of shoulder or elbow surgery participating in high school swimming, volleyball, or tennis. INTERVENTION(S) Participants were measured for all dependent variables at preseason and postseason. MAIN OUTCOME MEASURE(S) Participants were measured for glenohumeral IR and ER with the scapula stabilized. Total glenohumeral range of motion was calculated as the sum of IR and ER. Scapular upward rotation was measured at 0 degrees , 60 degrees , 90 degrees , and 120 degrees of glenohumeral abduction in the scapular plane, and scapular protraction was measured at 0 degrees , 45 degrees (hands on hips), and 90 degrees of glenohumeral abduction. RESULTS Internal rotation decreased from preseason to postseason (P = .012). Swimmers had less IR than both volleyball and tennis players (P = .001). External rotation also decreased in the swimmers (P = .001). Overall, preseason to postseason total motion decreased for athletes participating in swimming (P = .001) and tennis (P = .019). For all participants, preseason to postseason scapular protraction at 45 degrees glenohumeral abduction decreased (P = .007). CONCLUSIONS Female overhead athletes demonstrated decreases in IR after only one competitive season. Clinically, our results indicate that overhead athletes should be monitored for motion changes throughout their competitive seasons.

Prophylactic Ankle Braces and Star Excursion Balance Measures in Healthy Volunteers

CONTEXT The effects of prophylactic ankle braces on lower extremity functional performance in healthy participants have not been studied extensively. OBJECTIVE To determine if prophylactic ankle braces affected multidirectional reach distances during a test of dynamic balance. DESIGN Crossover. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Thirty-six healthy, physically active volunteers (18 men, 18 women; age = 23.6 +/- 2.7 years, height = 173.8 +/- 9.3 cm, mass = 74.4 +/- 12.7 kg, reach-leg length = 91.9 +/- 5.1 cm). INTERVENTION(S) Volunteers performed balance testing in 3 conditions: unbraced, while wearing a semirigid ankle brace, and while wearing a lace-up ankle brace. MAIN OUTCOME MEASURE(S) We used the Star Excursion Balance Test, calculating the mean of 3 attempts in 8 directions (anterior, anterior-medial, medial, posterior-medial, posterior, posterior-lateral, lateral, and anterior-lateral), normalized by the participants reach-leg length. Data were collected after 6 practice attempts for each of the conditions according to a balanced Latin square. RESULTS Bracing condition had no effect (P > .05) on any of the Star Excursion Balance Test directional measures. The largest mean difference due to bracing was 2.5% between the lace-up brace condition and the control in the posterior reach direction. This indicates that the actual reach differences due to bracing were less than 5.08 cm (2 inches) in length. CONCLUSIONS Clinicians can be confident that the prophylactic use of ankle braces does not disrupt lower extremity dynamic balance during a reaching task in healthy participants.

Gender comparisons of dynamic restraint and motor skill in children.

Objectives:To assess differences in neuromuscular dynamic restraint between high-skilled and low-skilled prepubescent girls and boys. To determine the contribution of sport experience and physical characteristics to motor skill. Subjects:Nineteen girls and 17 boys (8.89-9.40 y) participated. Intervention:Isometric hamstring and quadriceps muscle strength was assessed. Subjects performed 3 landing trials for measurement of preparatory EMG and vertical leg stiffness. Motor skill was assessed through analysis of 12 fundamental tasks. Sport experience was reported as hours per week and total years in organized and nonorganized activity. Outcome Measures:Dynamic restraint variables of isometric strength, preparatory EMG activity, and vertical leg stiffness were measured between groups. The contributions of time in sport, type of sport, and physical characteristics on skill were analyzed. Results:No significant gender or skill differences were found in quadriceps strength (P = 0.73), hamstring strength (P = 0.96), hamstring-to-quadriceps ratio (P = 0.71), or vertical leg stiffness (P = 0.38). Low-skilled children exhibited significantly greater (47.8%) preparatory hamstring-quadriceps coactivation than high-skilled subjects (P = 0.03). Participation in organized and nonorganized sport accounted for 29% of the variance in motor skill. Conclusions:Neuromuscular differences between genders were not observed, but dynamic restraint EMG measures differed between skill levels. The factors predisposing females to noncontact injuries may develop prepuberty to postpuberty from a combination of variables. Greater coactivation in the low-skilled group appears consistent with immature feedforward neuromuscular control strategies. These unrefined motor skills are less economical, may compromise dynamic restraint, and appear partially determined by sport experience.

Stiffness Regulation and Muscle-Recruitment Strategies of the Shoulder in Response to External Rotation Perturbations

BACKGROUND The complex interactions between capsuloligamentous structures and muscle-recruitment strategies that maintain glenohumeral stability remain unclear. The purposes of the present study were to determine whether stiffness regulation and muscle-activation strategies differed under varying joint positions and levels of contraction in the shoulder and to determine the relationship between generalized joint laxity, glenohumeral joint laxity, and joint stiffness. METHODS Forty healthy, physically active subjects with a mean age (and standard deviation) of 25.2 +/- 4.6 years, a mean height of 174.7 +/- 6.7 cm, and a mean mass of 73.1 +/- 13.8 kg were tested. Shoulder stiffness and the activation of muscles (including the rotator cuff and the anterior deltoid) were measured at two levels of internal rotation torque (0% and 50% of maximum) and two joint positions (0 degrees and 90% of maximum external rotation) before and after a 5 degrees external rotation perturbation. Generalized laxity and glenohumeral joint laxity (in the anterior, posterior, and inferior directions) were also assessed. RESULTS Stiffness was 77% greater at 50% of maximum internal rotation torque than at 0% of maximum internal rotation torque (p < 0.001) but was not significantly different between joint positions (p = 0.73). From 0% to 50% of maximum internal rotation torque, preparatory and reactive recruitment of the subscapularis increased significantly more (p < 0.05) than those of the other muscles. Also, subscapularis preparatory activity was 36% greater in 0 degrees of external rotation than in 90% of maximum external rotation (p < 0.01). Generalized joint laxity (as indicated by a score of >/=4) was present in 20% of the subjects. Glenohumeral joint laxity (as indicated by a grade of >/=2) was present in the anterior, posterior, and inferior directions in 13%, 15%, and 15% of the subjects, respectively. No correlation existed between passive stiffness and generalized or glenohumeral laxity (r = -0.12 to 0.29; p = 0.08 to 0.48). CONCLUSIONS Moderate levels of muscle contraction can significantly increase glenohumeral joint stiffness and stability. Preactivation of the subscapularis appears to be the primary dynamic stabilizer with the arm in 0 degrees of external rotation. However, with the arm in 90% of maximum external rotation (the apprehension position), less subscapularis activity is observed and the maintenance of stability may shift toward other musculoskeletal structures because joint stiffness does not change. A relationship between generalized joint laxity, glenohumeral laxity, and stiffness was not observed in healthy subjects.

Anatomical and Biomechanical Assessments of Medial Tibial Stress Syndrome

BACKGROUND Medial tibial stress syndrome is a common overuse injury in weightbearing, physically active individuals and in athletes. Most research associated with this condition is primarily based on static foot and lower-extremity measurements. METHODS A cross-sectional design was used to assess a set of static and dynamic measurements to determine which anatomical factors (limb length, ankle dorsiflexion, first metatarsophalangeal joint extension, and arch height) and biomechanical factors (center-of-pressure excursion index, malleolar valgus index, and gait velocity) are associated with medial tibial stress syndrome. RESULTS One-way analysis of variance models revealed that participants with medial tibial stress syndrome had significantly greater visual analog pain levels and slower gait velocity than noninjured controls (P = .05). No other significant differences were found between the two groups. CONCLUSIONS Further investigation of these and other factors can help health professionals develop better strategies for the prevention and clinical intervention of medial tibial stress syndrome.