Michael R. Torry

Gender differences in lower extremity kinematics, kinetics and energy absorption during landing

OBJECTIVE To determine whether gender differences exist in lower extremity joint motions and energy absorption landing strategies between age and skill matched recreational athletes. DESIGN Mixed factor, repeated measures design. BACKGROUND Compared to males, females execute high demand activities in a more erect posture potentially predisposing the anterior cruciate ligament to greater loads and injury. The preferred energy absorption strategy may provide insight for this performance difference. METHODS Inverse dynamic solutions estimated lower extremity joint kinematics, kinetics and energetic profiles for twelve males and nine females performing a 60 cm drop landing. RESULTS Females demonstrated a more erect landing posture and utilized greater hip and ankle joint range of motions and maximum joint angular velocities compared to males. Females also exhibited greater energy absorption and peak powers from the knee extensors and ankle plantar-flexors compared to the males. Examinations of the energy absorption contributions revealed that the knee was the primary shock absorber for both genders, whereas the ankle plantar-flexors muscles was the second largest contributor to energy absorption for the females and the hip extensors muscles for the males. CONCLUSIONS Females may choose to land in a more erect posture to maximize the energy absorption from the joints most proximal to ground contact. RELEVANCE Females may be at a greater risk to anterior cruciate ligament injury during landing due to their energy absorption strategy.

Model Prediction of Anterior Cruciate Ligament Force during Drop-Landings

PURPOSE The aim of this study was to calculate and explain the pattern of force transmitted to the anterior cruciate ligament during soft-style drop-landings. We hypothesized that peak ACL loading is due to the anterior pull of the quadriceps on the tibia, as these muscles develop large eccentric forces upon impact. METHODS A three-dimensional model of the body was used to simulate drop-landing. The simulation was performed by entering into the model muscle excitation patterns based on experimental EMG. The input excitation patterns were modified to create a performance response of the model that matched experimental data. Joint angles, ground reaction forces, and muscle forces obtained from the landing simulation were then applied to a model of the lower limb that incorporated a three-dimensional model of the knee. RESULTS The model ACL was loaded only in the first 25% of the landing phase. Peak ACL force (approximately 0.4 BW) resulted from a complex interaction between the patellar tendon force, the compressive force acting at the tibiofemoral joint, and the force applied by the ground to the lower leg. The patellar tendon force and tibiofemoral contact force both applied significant anterior shear forces to the shank throughout the landing phase. These effects were modulated by another significant posterior shear force applied by the ground reaction, which served to limit the maximum force transmitted to the ACL. CONCLUSION The pattern of ACL force in drop-landing cannot be explained by the anterior pull of the quadriceps force alone.

Biomechanics of the Shoulder in Youth Baseball Pitchers Implications for the Development of Proximal Humeral Epiphysiolysis and Humeral Retrotorsion

Background The effects of repetitive throwing on the shoulders of developing athletes are not well understood because of the paucity of data describing the biomechanics of youth pitchers and the plasticity of the developing skeleton. Hypothesis The direction and magnitude of the stresses that exist at the proximal humeral physis during the fastball pitching motion are consistent with the development of proximal humeral epiphysiolysis (Little League shoulder) and/or humeral retrotorsion. Study Design Descriptive laboratory study. Methods A total of 14 elite youth baseball pitchers (mean age, 12.1 ± 0.4 years) were filmed from the front and dominant side while throwing fastballs in a simulated game. The net force and torque acting on the humerus throughout the throwing motion were calculated using standard biomechanical techniques. Results The external rotation torque about the long axis of the humerus reached a peak value of 17.7 ± 3.5 N.m (2.7% ± 0.3% body weight × height) just before maximum shoulder external rotation. A shoulder distraction force of 214.7 ± 47.2 N (49.8% ± 8.3% body weight) occurred at, or just after, ball release. Conclusion Shear stress arising from the high torque late in the arm-cocking phase is large enough to lead to deformation of the weak proximal humeral epiphyseal cartilage, causing either humeral retrotorsion or proximal humeral epiphysiolysis over time. The stresses generated by the external rotation torque are much greater than those caused by distraction forces generated during the pitching motion of youth baseball pitchers. Clinical Relevance The motion of throwing fastballs by youth baseball pitchers results in force components consistent with proposed mechanisms for 2 clinical entities.

Gender Differences in Lower Extremity Landing Mechanics Caused by Neuromuscular Fatigue

Background Neuromuscular fatigue has been suggested as an extrinsic factor in the mechanism of noncontact anterior cruciate ligament injury in both genders. Purpose To determine and describe the lower extremity kinematic and kinetic differences caused by neuromuscular fatigue during drop landings and compare changes between age- and skill-matched male and female athletes. Methods Inverse dynamic solutions estimated lower extremity flexion-extension and varus-valgus kinematics and kinetics for 14 female and 16 male athletes performing a single-legged 50-cm drop landing. Subjects performed landings prefatigue and postfatigue with fatigue induced via a parallel squat exercise (60% of 1 repetition maximum) until failure. A mixed-model, repeated-measures analysis of variance (fatigue * gender) was performed on select kinematic and kinetic variables. Results Neuromuscular fatigue caused men and women to land with more hip flexion (main effect fatigue, P = .012; main effect gender, P = .001). Men exhibited greater peak knee flexion angles postfatigue; women did not alter knee flexion (fatigue * gender, P =.028). Men exhibited larger peak knee varus angles irrespective of fatigue (main effect gender, P = .039; main effect fatigue, P = .127; fatigue * gender, P = .153); women demonstrated larger peak valgus angles overall (main effects gender, P = .009). There were no changes with fatigue (main effect fatigue, P = .127) or a different response due to fatigue with gender (fatigue * gender, P = .091). Women exhibited greater knee anterior shear force postfatigue (fatigue * gender, P = .010). Men and women exhibited lower knee extension moments (main effect fatigue, P = .000; main effect gender, P = .927; fatigue * gender, P = .309) and abduction moments (main effect fatigue, P = .014; main effect gender, P = .670; fatigue * gender, P = .191). Conclusion Neuromuscular fatigue caused significant alterations in women that may be indicative of the noncontact anterior cruciate ligament injury mechanisms. Clinical Relevance Current noncontact anterior cruciate ligament prevention programs should incorporate a fatigue component to help minimize the deleterious effects of neuromuscular fatigue on landing mechanics.

Intra-articular knee joint effusion induces quadriceps avoidance gait patterns.

OBJECTIVES (1) To identify adaptations caused by intra-articular knee joint effusion during walking and (2) to determine if knee joint effusion may be a causative factor in promoting quadriceps avoidance gait patterns. DESIGN Gait testing of 14 healthy individuals who underwent incremental saline injections of the knee joint capsule.Background. Gait adaptations have been reported in the literature for knee injured and rehabilitating individuals. Knee joint capsular afferent activity can influence knee joint function. METHODS Gait analysis was employed in a pre- and post-test, repeated measures design to determine lower extremity joint kinematics, kinetics, energetics and thigh EMG adaptations due to intra-articular knee joint effusion. RESULTS Knee effusion caused an increase in hip and knee flexion through the stance phase. Knee extensor torque, impulse and negative and positive work were diminished with increased effusion levels. Quadriceps activity decreased and hamstring activity increased due to intra-articular knee joint effusion. DISCUSSION These adaptations cannot be attributed to an injury, surgery or rehabilitation. Thus, the results of this experiment suggest knee joint capsular distention, via knee joint effusion, may be responsible for many gait adaptations reported for knee injured individuals in previous investigations. CONCLUSIONS Knee joint effusion and the subsequent capsular distention can cause major alterations in the normal gait cycle and can be considered a causative factor promoting the acquisition of quadriceps avoidance gait patterns. RELEVANCE This study provides reference data on the effects of intra-articular knee joint effusion on gait parameters by which future studies of injured or rehabilitating individuals can be compared.

Gait adaptations before and after anterior cruciate ligament reconstruction surgery

Gait analyses of rehabilitated individuals with anterior cruciate ligament (ACL) deficiency and reconstruction have identified the final adaptations of increased hip extensor torque and hamstring electromyography (EMG) and decreased knee extensor torque and quadriceps EMG during stance. The initial adaptations to injury and surgery are, however, unknown as are the factors that influence the development of the adaptations. Identification of the initial response to injury would provide a basis for determining whether the final adaptations are learned automatically or if they are the result of a lengthy training period in which various factors may affect their development. The purpose of the study was to evaluate the initial effects of ACL injury and reconstruction surgery on joint kinematics, kinetics, and energetics, during walking. Injured limbs from nine subjects with ACL injury were tested 2 wk after injury, and 3 and 5 wk after surgery. Ten healthy subjects were tested. Kinematic and ground reaction data were collected and combined with inverse dynamics to calculate the joint torques and powers. A knee extensor torque throughout most of stance was observed in the injured limbs at all test sessions. This result was in conflict with previous observations of reduced extensor torque or a flexor torque in rehabilitated patients with ACL reconstruction and patients with ACL deficiency. This result also differed from the typical midstance extensor then flexor torque in healthy control subjects. Trend analysis showed a significant (P < 0.001) change in average position at the hip and knee, extensor angular impulse at the hip, and positive work done at the hip 3 wk after surgery followed by a partial rehabilitation at 5 wk after surgery. Power and work produced at the knee were reduced fivefold (P < 0.001) after 5 wk of rehabilitation and did not recover to pre-surgical levels. The existence of a long-lasting knee extensor torque 2 wk after injury indicated that the adaptation process to ACL deficiency is lengthy, requiring many gait cycles, and that numerous factors could be involved in learning the adaptations.

Effects of walking poles on lower extremity gait mechanics.

PURPOSE The purpose of this study was to determine whether walking with poles reduces loading to the lower extremity during level over ground walking. METHODS Three-dimensional gait analysis was conducted on 13 healthy adults who completed 10 walking trials using three different poling conditions (selected poles, poles back, and poles front) and without the use of poles (no poles). The inverse dynamics approach was used to calculate kinetic data via anthropometric, kinematic, and kinetic data. RESULTS All walking with poles conditions increased walking speed (P = 0.0001-0.0004), stride length (P < 0.0001), and stance time (P < 0.0001) compared with the no poles condition. There also was a decrease in anterior-posterior GRF braking impulse (P = 0.0001), a decrease in average vertical GRF walking with poles (P < 0.0001-0.0023), and a decrease in vertical (compressive) knee joint reaction force (P < 0.0001-0.0041) compared with the no poles condition. At the knee, extensor impulse decreased a 7.3% between the no poles and selected poles conditions (P = 0.0083-0.0287) and 10.4% between the no poles and poles back conditions (P < 0.0001). The support moment was reduced between the no poles and poles back (P = 0.0197) and poles front (P = 0.0002) conditions. Ankle plantarflexor work (A2) was reduced in the poles-front condition (P = 0.0334), but no differences were detected in all other ankle, knee or hip power and work variables (P > 0.05). CONCLUSION There were differences in kinetic variables between walking with and without poles. The use of walking poles enabled subjects to walk at a faster speed with reduced vertical ground reaction forces, vertical knee joint reaction forces, and reduction in the knee extensor angular impulse and support moment, depending on the poling condition used.

The belly-press test for the physical examination of the subscapularis muscle: electromyographic validation and comparison to the lift-off test☆

The purpose of this study was to determine the validity of the belly-press test as a clinical test for the subscapularis muscle with the use of electromyography (EMG). In addition, the belly-press and lift-off tests were compared to determine whether the two physical examination techniques are equivalent in their evaluation of the upper and lower portions of the subscapularis muscle. EMG data of 7 muscles (upper subscapularis, lower subscapularis, infraspinatus, latissimus dorsi, teres major, pectoralis major, and supraspinatus) were studied in 16 healthy volunteers. Average EMG amplitudes were contrasted within and between tests. Both the belly-press and lift-off tests activated the upper and lower portions of the subscapularis muscle greater than all other muscles, indicating that both tests are valid and specific for evaluation of the subscapularis muscle (P <.05). The belly-press test was found to activate the upper subscapularis muscle significantly more than the lift-off test (P <.05), whereas the lift-off test was found to pose a significantly greater challenge to the lower subscapularis muscle than the belly-press test (P <.05). These findings may improve the clinical testing and assessment of the subscapularis muscle.

Humeral Torque in Professional Baseball Pitchers

Background Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion. Methods The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations. Results Peak humeral axial torque reached a mean value of 92 ± 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures. Conclusions Fractures are most likely to occur near the time of maximum shoulder external rotation when humeral torque peaks. Pitchers whose elbows were more extended at stride foot contact tended to have lower peak humeral torques.

Subscapularis Muscle Activity during Selected Rehabilitation Exercises

Background The upper and lower portions of the subscapularis muscle are independently innervated and activated. Hypothesis Upper and lower portions of the subscapularis muscle demonstrate different activation levels and require different exercises for rehabilitation. Study Design Controlled laboratory study. Methods Fifteen healthy subjects performed seven shoulder-strengthening exercises. Electromyographic data were collected from the latissimus dorsi, teres major, pectoralis major, infraspinatus, supraspinatus, and upper and lower subscapularis muscles. Results Upper subscapularis muscle activity was greater than lower subscapularis muscle activity for all exercises except for internal rotation with 0° of humeral abduction. The push-up plus and diagonal exercises consistently stressed the upper and lower subscapularis muscles to the greatest extent. Conclusions Humeral abduction was found to have a strong influence on the selective activation of the upper versus the lower subscapularis muscle and thus supported the design of different exercise continuums. In addition, the push-up plus and diagonal exercises were found to be superior to traditional internal rotation exercises for activating both functional portions of the subscapularis muscle. Clinical Relevance Our results showing that the upper and lower portions of the subscapularis muscle are functionally independent may affect training or rehabilitation protocols for the rotator cuff muscles.