Ian J. Kremenic

The objective of this study was to compare the spring-like properties of pelvis and trunk rotation during baseball pitching in high school pitchers with varying ball velocities. It was hypothesized that high-velocity pitchers would be more effective at accelerating the trunk on the pelvis from foot contact to ball release. Three-dimensional kinematics were recorded in 35 high school pitchers (age 16.5 ± 1.1 year, height 1.83 ± 0.06 m, body mass 82.8 ± 9.9 kg, and pitch velocity 75.0 ± 5.6 mph). Pelvis and trunk angular velocities and accelerations, and trunk–pelvis separation, were calculated and averaged for 3 pitches. Additionally, average trunk-on-pelvis acceleration was calculated from foot contact to ball release. Pitchers were classified as high-, average-, or low-velocity, and single-factor ANOVA was used to compare metrics between groups. Peak pelvis and trunk velocities were higher for high- versus low-velocity pitchers (p = 0.001 and p = 0.008, respectively). Pelvis deceleration was greater in high-velocity pitchers (p = 0.024), and average trunk-on-pelvis acceleration was greater for high-velocity pitchers (p = 0.013). Acceleration of the trunk on the pelvis during the baseball pitch quantifies the spring-like properties derived from pelvis and trunk kinematic sequencing. High-velocity pitchers more effectively release the spring by decelerating the pelvis prior to ball release.

The purpose of this study was to examine kinematic, kinetic, and muscle activation metrics during countermovement jumps (CMJs) with varying countermovement depths. The hypothesis was that a shallow countermovement depth would compromise jump height by disrupting neuromechanical control. Ten healthy men (age 26 ± 8 yr, height 1.81 ± 0.08 m, mass 83.5 ± 9.0 kg) performed maximal CMJs at self‐selected countermovement depth (self‐selected CMJ), at reduced countermovement depth (shallow CMJ), and at increased countermovement depth (deep CMJ). Three jumps were performed in each condition on force plates with ankle, knee, and hip motion recorded and electromyograms (EMG) recorded from the gluteus maximus (GM), vastus lateralis (VL), and medial gastrocnemius (MG) muscles. During CMJs, the knee flexion angle was recorded with an electrogoniometer. Jumpers were instructed to flex at least 15% less (shallow CMJ) and at least 15% more (deep CMJ) than the self‐selected CMJs. Kinematic, kinetic, and EMG metrics were compared between the different CMJ depths using repeated measures ANOVA. Compared with self‐selected CMJs, shallow CMJs had 26% less countermovement depth (P < 0.001, effect size 1.74) and the deep CMJs had 28% greater countermovement depth (P < 0.001, effect size 1.56). Jump height was 8% less for the shallow vs. self‐selected CMJs (P = 0.007, effect size 1.09) but not different between self‐selected and deep CMJs (P = 0.254). Shallow CMJs differed from self‐selected CMJs at the initiation of the countermovement (unweighting). For self‐selected CMJs, force dropped to 43% of body weight during unweighting but only to 58% for shallow CMJs (P = 0.015, effect size 0.95). During unweighting, VL EMG averaged 5.5% of MVC during self‐selected CMJs versus 8.1% for shallow CMJs (P = 0.014, effect size 0.97). Percent decline in jump height with shallow versus self‐selected CMJs was correlated with the difference in VL EMG during unweighting between shallow and self‐selected CMJs (r = 0.651, P = 0.041). A deep countermovement prolonged the time to execute the jump by 38% (P < 0.010, effect size 1.04) but did not impair CMJ force metrics. In conclusion, self‐selected countermovement depth represents a tradeoff between dropping the center of mass sufficiently far and executing the jump quickly. Unweighting at the initiation of a CMJ appears to be a critical element in the neuromechanics of the CMJ.

Purpose: To assess the utility of an inertial sensor for assessing recovery in professional soccer players. Methods: In a randomized, crossover design, 11 professional soccer players wore shorts fitted with phase change material (PCM) cooling packs or uncooled packs (control) for 3 h after a 90-min match. Countermovement jump (CMJ) performance was assessed simultaneously with an inertial sensor and an optoelectric system: prematch and 12, 36, and 60 h postmatch. Inertial sensor metrics were flight height, jump height, low force, countermovement distance, force at low point, rate of eccentric force development, peak propulsive force, maximum power, and peak landing force. The only optoelectric metric was flight height. CMJ decrements and the effect of PCM cooling were assessed with repeated-measures analysis of variance. Jump heights were also compared between devices. Results: For the inertial sensor data, there were decrements in CMJ height on the days after matches (88% [10%] of baseline at 36 h, P = .012, effect size = 1.2, for control condition) and accelerated recovery with PCM cooling (105% [15%] of baseline at 36 h, P = .018 vs control, effect size = 1.1). Flight heights were strongly correlated between devices (r = .905, P < .001), but inertial sensor values were 1.8 [1.8] cm lower (P = .008). Low force during countermovement was increased (P = .031) and landing force was decreased (P = .043) after matches, but neither was affected by the PCM cooling intervention. Other CMJ metrics were unchanged after matches. Conclusions: This small portable inertial sensor provides a practical means of assessing recovery in soccer players.

Repetition of jumps in dance and sport training poses a potential injury risk; however, non‐contact landing injuries are more common in athletes than dancers. This study aimed to compare the lower limb stiffness characteristics of dancers and athletes during drop landings to investigate possible mechanisms of impact‐related injuries. Kinematics and kinetics were recorded as 39 elite modern and ballet dancers (19 men and 20 women) and 40 college‐level team sport athletes (20 men and 20 women) performed single‐legged drop landings from a 30‐cm platform. Vertical leg stiffness and joint stiffness of the hip, knee, and ankle were calculated using a spring‐mass model. Stiffness data, joint kinematics, and moments were compared with a group‐by‐sex 2‐way analysis of variance. Multiple linear regression was used to assess the relative contribution of hip and knee and ankle joint stiffness to variance in overall vertical leg stiffness for dancers and athletes. Dancers had lower leg (P < 0.001), knee joint (P = 0.034), and ankle joint stiffness (P = 0.043) than athletes. This was facilitated by lower knee joint moments (P = 0.012) and greater knee (P = 0.029) and ankle joint (P = 0.048) range of motion in dancers. Males had higher leg (P < 0.001) and ankle joint stiffness (P < 0.001) than females. This occurred through lower ankle range of motion (P < 0.001) and greater ankle moment (P = 0.022) compared to females. Male and female dancers demonstrated reduced lower limb stiffness compared to athletes, indicating a more pliable landing technique. Dance training techniques could potentially inform approaches to injury prevention in athletes.

Traditionally, shoulder isometrics are introduced in the early stages of shoulder rehabilitation. A patient's isometric torque output is based on a subjective perception of force generation. By utilizing elastic resistance elongation (strain) to standardize force output, clinicians could prescribe shoulder therapeutic isometrics based on % maximum voluntary contraction (%MVC). The purpose of this study was to measure electromyographic (EMG) activity and determine the %MVC during shoulder flexion, external rotation and abduction isometrics at varying lengths of TheraBand® elastic resistance. It was hypothesized that increased elongation of progressive resistance bands would proportionately increase the %MVC of the shoulder musculature. Laboratory design using healthy subjects. Eight healthy subjects (16 shoulders) (5 females, 3 males; avg. age 29.2) were tested. Surface EMG electrodes were placed over the anterior deltoid, middle deltoid, and infraspinatus muscles. A force transducer was anchored to a stable surface with its corresponding end in series with an extremity strap securely holding the elastic band. Subjects were asked to maintain shoulder position for the proper isometric contraction (flexion, abduction and external rotation) while taking incremental steps away from the anchored elastic resistance, to the beat of a metronome to clearly marked distances on the floor (50, 100, 150, 200 and 250% of band elongation). This was repeated with yellow, red, green, and blue TheraBand® resistance levels. Maximum voluntary contractions for both force and EMG were collected for each subject in all three test positions. EMG data were normalized and expressed as a %MVC. For external rotation and flexion, the infraspinatus and anterior deltoid activity increased with band elongation (p<0.01) and progressive colors (p<0.01). The increases in EMG activity with elongation plateaued with the yellow and red bands but continued to increase with the green and blue bands (p<0.01). The increase in infraspinatus and anterior deltoid EMG activity with progressive band color was more apparent for green and blue bands compared with yellow and red band (p<0.01). For the abduction exercise, middle deltoid activity increased with band elongation (p<0.01) and progressive color (p<0.01). In all three exercises, there was an increase in force exerted by the band with increasing length and band color (p < 0.001). However, while there were clear increases in force from red to green to blue, there was no difference in force between yellow and red regardless of elongation (p<0.01). Isometric flexion, external rotation and abduction muscle activity can be accurately prescribed clinically by adjusting the elongation and resistance associated with progressive colors of resistance bands. 3.

Knee osteoarthritis is a prevalent disease. Unloading the affected compartment using a brace is a treatment option. To determine whether a decompressive knee brace alters loading in medial knee osteoarthritis following 2 and 8 weeks of use. Within subjects; pre- and post-testing. A total of 15 individuals with medial knee osteoarthritis attended four sessions: baseline, fitting, 2 weeks after fitting (post), and 8 weeks after fitting (final). A gait analysis was performed at baseline (without knee brace), post and final. Knee adduction impulse, first and second peak knee adduction moment, knee motion, and walking velocity were calculated. Participants also recorded hours and steps taken while wearing the brace. On average, the brace was worn for more than 6 h/day. Through use of repeated-measures analysis of variance, it was determined that the knee adduction impulse and second peak knee adduction moment were reduced (p < 0.05) at post and final compared to baseline (36% and 34% reduction in knee adduction impulse, 26% reduction in second peak knee adduction moment for post and final, respectively). Furthermore, participants walked faster with increased knee motion during stance. The studied decompressive brace was effective in reducing potentially detrimental forces at the knee—knee adduction impulse and second peak knee adduction moment during the stance phase of gait. The data from this study suggest that use of a medial unloading brace can reduce potentially detrimental adduction moments at the knee. Clinicians should use this evidence to advocate for use of this noninvasive treatment for people presenting with medial knee osteoarthritis.