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Bram L. Newman, Courtney L. Pollock and Michael A. Hunt

Context: Lateral trunk-flexion strength is an important determinant of overall trunk stability and function, but the reliability in measuring this outcome clinically in athletic individuals is not known. Objective: To determine the interrater and intrarater reliability of lateral trunk-flexion strength measurement in athletic individuals using handheld dynamometry. Design: Reliability study. Setting: Research laboratory. Participants: 12 healthy, athletic individuals. Intervention: Lateral trunk-flexion strength was measured using handheld dynamometry across 2 different trunk placements (lateral aspect of the axilla and laterally at the level of the midtrunk) and 2 testing occasions by 2 therapists. Three maximum-effort trials during a "make test" at each placement were completed for each therapist on both occasions. Main Outcome Measures: Maximum force output was identified and converted to a torque. Intraclass correlation coefficients (ICC2,1) were calculated for each dynamometer placement, therapist, and test occasion to determine intrarater and interrater reliability. Results: Intrarater reliability was moderate to good (ICC2,1 = .53-.77), while interrater reliability was good to very good (ICC2,1 = .79-81) at the axilla position. For the midtrunk position, intrarater reliability was good to very good (ICC2,1 = .80-.86), while interrater reliability was good on both days (ICC2,1 = .87-.88). Finally, the standard errors of measurement were low for the axilla position (0.20 Nm/kg; 95% CI .15, .28) and midtrunk position (0.09 Nm/kg; 95% CI .07, .12). Conclusions: Maximum lateral trunk-flexion strength can be reliably measured in athletic individuals with greater overall strength. Based on the 2 positions used in this study, measurement with a dynamometer placement at the midtrunk may be more reliable than that obtained at the axilla.

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Christopher Napier, Christopher L. MacLean, Jessica Maurer, Jack E. Taunton and Michael A. Hunt

High magnitudes and rates of loading have been implicated in the etiology of running-related injuries. Knowledge of kinematic variables that are predictive of kinetic outcomes could inform clinic-based gait retraining programs. Healthy novice female runners ran on a treadmill while 3-dimensional biomechanical data were collected. Kinetic outcomes consisted of vertical impact transient, average vertical loading rate, instantaneous vertical loading rate, and peak braking force. Kinematic outcomes included step length), hip flexion angle at initial contact, horizontal distance from heel to center of mass at initial contact, shank angle at initial contact, and foot strike angle. Stepwise multiple linear regression was used to evaluate the amount of variance in kinetic outcomes explained by kinematic outcomes. A moderate amount of variance in kinetic outcomes (vertical impact transient = 46%, average vertical loading rate = 37%, instantaneous vertical loading rate = 49%, peak braking force = 54%) was explained by several discrete kinematic variables—predominantly speed, horizontal distance from heel to center of mass, foot strike angle, and step length. Hip flexion angle and shank angle did not contribute to any models. Decreasing step length and transitioning from a rearfoot strike may reduce kinetic risk factors for running-related injuries. In contrast, clinical strategies such as modifying shank angle and hip flexion angle would not appear to contribute significantly to the variance of kinetic outcomes after accounting for other variables.

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Courtney L. Pollock, Michael A. Hunt, Taian M. Vieira, Alessio Gallina, Tanya D. Ivanova and S. Jayne Garland

Background: Ankle plantarflexor muscle impairment contributes to asymmetrical postural control poststroke. Objective: This study examines the relationship of plantarflexor electromyography (EMG) with anterior–posterior center of pressure (APCOP) in people poststroke during progressive challenges to standing balance. Methods: Ten people poststroke and 10 controls participated in this study. Anteriorly directed loads of 1% body mass (BM) were applied to the pelvis every 25–40 s until 5%BM was reached. Cross-correlation values between plantarflexor EMG and APCOP (EMG:APCOP) position and velocity were compared. Results: EMG:APCOP velocity correlations were stronger than EMG:APCOP position across all muscles (p < .01), and correlations were predominately stronger in the nonparetic compared with the paretic leg (p < .05). Increasing challenge to standing balance reduced asymmetry of EMG:APCOP relationships. Conclusions: These data suggest that sensory information reflected in APCOP velocity interacts more strongly with plantarflexor activity in people poststroke and controls than APCOP position. Furthermore, increasing challenge to standing balance reduces postural control asymmetry between legs poststroke.