Michael P. McNally

The effects of core muscle activation on dynamic trunk position and knee abduction moments: Implications for ACL injury

Anterior cruciate ligament (ACL) injury is one of the most common serious lower-extremity injuries experienced by athletes participating in field and court sports and often occurs during a sudden change in direction or pivot. Both lateral trunk positioning during cutting and peak external knee abduction moments have been associated with ACL injury risk, though it is not known how core muscle activation influences these variables. In this study, the association between core muscle pre-activation and trunk position as well as the association between core muscle pre-activation and peak knee abduction moment during an unanticipated run-to-cut maneuver were investigated in 46 uninjured individuals. Average co-contraction indices and percent differences between muscle pairs were calculated prior to initial contact for internal obliques, external obliques, and L5 extensors using surface electromyography. Outside tilt of the trunk was defined as positive when the trunk was angled away from the cutting direction. No significant associations were found between pre-activations of core muscles and outside tilt of the trunk. Greater average co-contraction index of the L5 extensors was associated with greater peak knee abduction moment (p=0.0107). Increased co-contraction of the L5 extensors before foot contact could influence peak knee abduction moment by stiffening the spine, limiting sagittal plane trunk flexion (a motion pattern previously linked to ACL injury risk) and upper body kinetic energy absorption by the core during weight acceptance.

Hip adductor activations during run-to-cut manoeuvres in compression shorts: implications for return to sport after groin injury

Abstract Athletes at high risk of groin strains in sports such as hockey and soccer often choose to wear shorts with directional compression to aid in prevention of or recovery from hip adductor strains. Large, eccentric contractions are known to result in or exacerbate strain injuries, but it is unknown if these shorts have a beneficial effect on hip adductor muscle activity. In this study, surface electromyography (EMG) of the adductor longus and ground reaction force (GRF) data were obtained simultaneously on 29 healthy individuals without previous history of serious injury while performing unanticipated 45° run-to-cut manoeuvres in a laboratory setting wearing shorts with non-directional compression (control, HeatGear, Under Armour, USA) or shorts with directional compression (directional, CoreShort PRO, Under Armour, USA), in random order. Average adductor activity in the stance leg was significantly lower in the directional condition than in the control condition during all parts of stance phase (all P < 0.042). From this preliminary analysis, wearing directional compression shorts appears to be associated with reduced stance limb hip adductor activity. Athletes seeking to reduce demand on the hip adductors as they approach full return to activities may benefit from the use of directional compression shorts.

Hamstring Strength Asymmetry at 3 Years After Anterior Cruciate Ligament Reconstruction Alters Knee Mechanics During Gait and Jogging

Background: Anterior cruciate ligament reconstruction (ACLR) using a hamstring tendon autograft often results in hamstring muscle strength asymmetry. However, the effect of hamstring muscle strength asymmetry on knee mechanics has not been reported. Hypothesis: Participants with hamstring strength asymmetry would demonstrate altered involved limb knee mechanics during walking and jogging compared with those with more symmetric hamstring strength at least 2 years after ACLR with a hamstring tendon autograft. Study Design: Controlled laboratory study. Methods: There were a total of 45 participants at least 2 years after ACLR (22 male, 23 female; mean time after ACLR, 34.6 months). A limb symmetry index (LSI) was calculated for isometric hamstring strength to subdivide the sample into symmetric hamstring (SH) (LSI ≥90%; n = 18) and asymmetric hamstring (AH) (LSI <85%; n = 18) groups. Involved knee kinematic and kinetic data were collected using 3-dimensional motion analysis during gait and jogging. Peak sagittal-, frontal-, and transverse-plane knee angles and sagittal-plane knee moments and knee powers were calculated. Independent-samples t tests and analyses of covariance were used to compare involved knee kinematic and kinetic variables between the groups. Results: There were no differences in sagittal- and frontal-plane knee angles between the groups (P > .05 for all). The AH group demonstrated decreased tibial internal rotation during weight acceptance during gait (P = .01) and increased tibial external rotation during jogging at initial contact (P = .03) and during weight acceptance (P = .02) compared with the SH group. In addition, the AH group demonstrated decreased peak negative knee power during midstance (P = .01) during gait compared with the SH group, after controlling for gait speed, which differed between groups. Conclusion: Participants with hamstring strength asymmetry showed altered involved knee mechanics in the sagittal plane during gait and in the transverse plane during gait and jogging compared with those with more symmetric hamstring strength. Clinical Relevance: Hamstring strength asymmetry is common at 3 years after ACLR with a hamstring tendon autograft and affects involved knee mechanics during gait and jogging. Additional research is warranted to further investigate the longitudinal effect of these alterations on knee function and joint health after ACLR.

Lower Extremity Work Is Associated with Club Head Velocity during the Golf Swing in Experienced Golfers

While the golf swing is a complex whole body movement requiring coordination of all joints to achieve maximum ball velocity, the kinetic contribution of the lower extremities to club head velocity has not been quantified, despite the perception that the legs are a primary source of power during the swing. Mechanical power at the hips, knees, and ankles was estimated during the downswing phase of a full swing with a driver using a passive optical motion capture system and 2 force plates for adult males across a range of age and self-reported skill levels. Total work by the lower extremities was calculated by integrating the powers of all 6 joints over the downswing. Regression analyses showed that total lower extremity work was a strong predictor of club head velocity (R=0.63). Secondary analyses showed different relationships to club head velocity in lead and trail leg lower extremity joints, but none of these were as predictive of club head velocity as the total work performed by the lower extremities. These results provide quantitative evidence that the lower bodys kinetic contribution may be an important factor in achieving greater club head velocity, contributing to greater driving distance and overall golf performance.

Quadriceps and Hamstrings Strength in Athletes

Quadriceps and hamstrings strength is usually quantified by the peak torque during maximal voluntary isokinetic contractions. Ratios of peak torque are used to assess limb asymmetry and compare hamstrings strength relative to quadriceps strength. Peak torque is affected by the mode and speed of testing, and it is important to consider whether or not to normalize peak torque (e.g., to body mass). Positive, but moderate correlations were observed between knee strength and triple hop distance and between knee strength and hip strength in a population of collegiate freshmen football players. No significant correlations were observed between knee strength and Functional Movement Screen™ performance, or between limb symmetry indices based on different strength and functional tests. Deficiencies in quadriceps and hamstrings strength may increase the risk of lower extremity injuries, but large prospective studies are needed to determine which measures of strength are the best predictors for specific injuries and to optimize injury prevention strategies.

Stride Leg Ground Reaction Forces Predict Throwing Velocity in Adult Recreational Baseball Pitchers.

Abstract McNally, MP, Borstad, JD, Oñate, JA, and Chaudhari, AMW. Stride leg ground reaction forces predict throwing velocity in adult recreational baseball pitchers. J Strength Cond Res 29(10): 2708–2715, 2015—Ground reaction forces produced during baseball pitching have a significant impact in the development of ball velocity. However, the measurement of only one leg and small sample sizes in these studies curb the understanding of ground reaction forces as they relate to pitching. This study aimed to further clarify the role ground reaction forces play in developing pitching velocity. Eighteen former competitive baseball players with previous high school or collegiate pitching experience threw 15 fastballs from a pitchers mound instrumented to measure ground reaction forces under both the drive and stride legs. Peak ground reaction forces were recorded during each phase of the pitching cycle, between peak knee height and ball release, in the medial/lateral, anterior/posterior, and vertical directions, and the peak resultant ground reaction force. Stride leg ground reaction forces during the arm-cocking and arm-acceleration phases were strongly correlated with ball velocity (r 2 = 0.45–0.61), whereas drive leg ground reaction forces showed no significant correlations. Stepwise linear regression analysis found that peak stride leg ground reaction force during the arm-cocking phase was the best predictor of ball velocity (r 2 = 0.61) among drive and stride leg ground reaction forces. This study demonstrates the importance of ground reaction force development in pitching, with stride leg forces being strongly predictive of ball velocity. Further research is needed to further clarify the role of ground reaction forces in pitching and to develop training programs designed to improve upper extremity mechanics and pitching performance through effective force development.

Muscle co-contraction during gait in individuals with articular cartilage defects in the knee

Increased muscle co-contraction during gait is common in individuals with knee pathology, and worrisome as it is known to amplify tibiofemoral compressive forces. While knees with articular cartilage defects (ACD) are more vulnerable to compressive forces, muscle co-contraction has never been reported in this population. The purpose of this study was to evaluate the extent to which individuals with ACDs in the knee demonstrate elevated quadriceps to hamstrings muscle co-contraction on the involved limb during gait compared to the uninvolved limb and to healthy controls. We also explored the impact of participant characteristics and knee impairments on co-contraction. Twenty-nine individuals with full-thickness knee ACDs (ACD group) and 19 healthy adults (control group) participated in this study. Participants performed five gait trials at self-selected speed, during which activity of the quadriceps and hamstrings muscles were collected with surface electromyography. Three-dimensional motion capture was used to define phases of gait. Quadriceps strength and self-reported outcomes were also assessed in the same session. There were no differences in quadriceps: hamstrings co-contraction between the ACD and control groups, or between the involved and uninvolved limb for the ACD group. For both ACD and control groups, co-contraction was highest in early stance and lowest in late stance. Quadriceps strength was consistently the strongest predictor of muscle co-contraction in both the ACD and the control groups, with individuals with lower strength demonstrating greater co-contraction. Further study is needed to understand the effect of increased muscle co-contraction on joint compressive forces in the presence of varied quadriceps strength.

Portable Myoelectric Brace Use Increases Upper Extremity Recovery and Participation But Does Not Impact Kinematics in Chronic, Poststroke Hemiparesis

ABSTRACT The authors examined the efficacy of an 8-week regimen combining repetitive task-specific practice (RTP) with a myoelectric brace (RTP+Myomo) on paretic upper extremity (UE; use in valued activities, perceived recovery, and reaching kinematics) in 12 subjects (4 men; M age = 53.5 years; mean time poststroke = 61.7 months). Seven subjects were administered RTP+Myomo therapy, and 5 were administered RTP only. Both groups participated in individualized, 45-min therapy sessions occurring 3 days/week over an 8-week period. The arm, hand ability, activities of daily living, and perceptions of recovery subscales of the Stroke Impact Scale (SIS), as well as UE reaching kinematics, assessed before and after the intervention. Subjects in the RTP+Myomo group showed greater improvements on all SIS subscales, with the recovery scale reaching statistical significance (p = .03). Subjects in the RTP-only group showed a greater increase in hand velocity in the reach up task (p = .02), but no changes were observed in the range of shoulder flexion or elbow extension during reaching. None of the changes in kinematic outcome measures significantly correlated with any of the changes in SIS subscales. RTP integrating myoelectric bracing may be more beneficial than RTP only in improving self-reported function and perceptions of overall recovery. The authors observed no changes in the range of elbow extension, and no relationship between self-reported improvements and changes in reaching kinematics.

Changes in Throwing Arm Mechanics at Increased Throwing Distances During Structured Long-Toss:

Background: Elbow injuries among adolescent baseball players have been outpacing those of college and professional players. In attempts to prevent injuries and maximize return-to-play potential following injury, attention has been focused on “return to throw” programs, which include long-toss throws. Because the few studies that were conducted on long-toss throwing focused primarily on college-aged athletes, it is not known what type of load is incurred at the elbow during interval throwing progression among high school baseball players. Purpose: To quantify the change in arm slot, arm speed, shoulder external rotation, and elbow varus torque across increasing throwing distances within a given athlete. Study Design: Descriptive laboratory study. Methods: Ninety-five high school baseball players performed a long-toss protocol while wearing an inertial sensor and sleeve. Each participant was tested for 5 throws at distances of 9 m, 18 m, 27 m, 37 m, and 46 m. Linear mixed-effects models and likelihood ratio tests were used to estimate the within-participant relationship between throw distance and arm slot, arm speed, shoulder external rotation, and elbow varus torque. Results: Arm slot (P < .01), arm speed (P < .01), shoulder external rotation (P < .01), and elbow varus torque (P < .01) were significantly associated with long-toss throw distance. As the throw distance increased, there was an increase in arm speed and shoulder external rotation and a decrease in arm slot for each distance. However, elbow varus torque increased with each distance up to 37 m and then remained the same at 46 m. Conclusion: The use of longer distances for conditioning and rehabilitation may be beneficial in increasing shoulder range of motion and arm speed; however, precaution needs to be taken, as throwing longer distances are accompanied by an increase in arm rotation, arm speed, and elbow torque, with a decrease in arm slot. Clinical Relevance: Return-to-throw programs have been utilized by sports medicine clinicians and coaches to help guide a player during rehabilitation. These programs involve throwing at increased efforts through increased distances with no immediate feedback on elbow stress. This investigation describes arm biomechanical changes during submaximum interval throwing and demonstrates a tool that can be utilized to measure arm stress in real time for clinicians and athletes progressing through an interval throwing program.

Validation of a method to accurately correct anterior superior iliac spine marker occlusion

Anterior superior iliac spine (ASIS) marker occlusion commonly occurs during three-dimensional (3-D) motion capture of dynamic tasks with deep hip flexion. The purpose of this study was to validate a universal technique to correct ASIS occlusion. 420 ms of bilateral ASIS marker occlusion was simulated in fourteen drop vertical jump (DVJ) trials (n=14). Kinematic and kinetic hip data calculated for pelvic segments based on iliac crest (IC) marker and virtual ASIS (produced by our algorithm and a commercial virtual join) trajectories were compared to true ASIS marker tracking data. Root mean squared errors (RMSEs; mean±standard deviation) and intra-class correlations (ICCs) between pelvic tracking based on virtual ASIS trajectories filled by our algorithm and true ASIS position were 2.3±0.9° (ICC=0.982) flexion/extension, 0.8±0.2° (ICC=0.954) abduction/adduction for hip angles, and 0.40±0.17 N m (ICC=1.000) and 1.05±0.36 N m (ICC=0.998) for sagittal and frontal plane moments. RMSEs for IC pelvic tracking were 6.9±1.8° (ICC=0.888) flexion/extension, 0.8±0.3° (ICC=0.949) abduction/adduction for hip angles, and 0.31±0.13 N m (ICC=1.00) and 1.48±0.69 N m (ICC=0.996) for sagittal and frontal plane moments. Finally, the commercially-available virtual join demonstrated RMSEs of 4.4±1.5° (ICC=0.945) flexion/extension, 0.7±0.2° (ICC=0.972) abduction/adduction for hip angles, and 0.97±0.62 N m (ICC=1.000) and 1.49±0.67 N m (ICC=0.996) for sagittal and frontal plane moments. The presented algorithm exceeded the a priori ICC cutoff of 0.95 for excellent validity and is an acceptable tracking alternative. While ICCs for the commercially available virtual join did not exhibit excellent correlation, good validity was observed for all kinematics and kinetics. IC marker pelvic tracking is not a valid alternative.