Oscillation and Reaction Board Techniques for Estimating Inertial Properties of a Below-knee Prosthesis

The purpose of this study was two-fold: 1) demonstrate a technique that can be used to directly estimate the inertial properties of a below-knee ...

University of Northern Colorado

Recent attention given to the mechanical work of the lower extremity joints, the emerging importance of the stance phase of running, and the lack of consensus regarding the biomechanical correlates to economical running were primary justifications for this study. The purpose of this experiment was to identify the correlations between metabolic power and the positive and negative mechanical work at lower extremity joints during stance. Recreational runners (n = 16) ran on a treadmill at 3.35 m s(-1) for physiological measures and overground for biomechanical measures. Inverse dynamics were used to calculate net joint moments and powers at the ankle, knee, and hip. Joint powers were then integrated over the stance phase so that positive and negative joint mechanical work were correlated with metabolic power (r = 0.60-0.69). Positive work at the hip and ankle during stance was positively correlated to metabolic power. In addition to these results, more economical runners (lower metabolic power) exhibited greater negative work at the hip, greater positive work at the knee, and less negative work at the ankle. Between the most and least economical runners, different mechanical strategies were present at the hip and knee, whereas the kinetics of the ankle joint differed only in magnitude.

Lower extremity mechanical work during stance phase of running partially explains interindividual variability of metabolic power.

The purpose of this study was to investigate the influence of weight distribution (WtD) asymmetry on the biomechanics of a barbell back squat. This study included 2 groups of trained individuals who were separated based on a WtD test (n = 14 in each group). They performed the barbell back squats with 2 resistance levels (60 and 75% of 1 repetition maximum) to measure vertical ground reaction force (GRF), tilting, and rotational angular bar displacements. A symmetry index (SI) score of the vertical GRF and the 2 bar displacements were examined to identify the group difference. Results showed that the unequal WtD group displayed a higher vertical GRF SI score (p < 0.05) and greater degrees of the tilting (p < 0.05) and rotational (p < 0.05) angular bar displacements. The 2 resistances did not influence the magnitude of the dependent variables, and no interactions were found. The unequal WtD captured at the WtD test carried over to the SI score during the back squat test. The unequal WtD was also a partial factor of displaying greater bar displacements. The lack of postural control to distribute body weight evenly should be treated properly to gain levelness before participating in high volume of resistance training, and coaches should be conscious of moving in a symmetrical fashion with minimal bar displacements in tilting and rotational manner.

Influence of weight distribution asymmetry on the biomechanics of a barbell back squat.

Dynamic stability is often measured by time to stabilization (TTS), which is calculated from the dwindling fluctuations of ground reaction force (GRF) components over time. Common protocols of dynamic stability research have involved forward or vertical jumps, neglecting different jump-landing directions. Therefore, the purpose of the present investigation was to examine the influence of different jump-landing directions on TTS. Twenty healthy participants (9 male, 11 female; age = 28 ± 4 y; body mass = 73.3 ± 21.5 kg; body height = 173.4 ± 10.5 cm) completed the Multi-Directional Dynamic Stability Protocol hopping tasks from four different directions--forward, lateral, medial, and backward--landing single-legged onto the force plate. TTS was calculated for each component of the GRF (ap = anterior-posterior; ml = medial-lateral; v = vertical) and was based on a sequential averaging technique. All TTS measures showed a statistically significant main effect for jump-landing direction. TTSml showed significantly longer times for landings from the medial and lateral directions (medial: 4.10 ± 0.21 s, lateral: 4.24 ± 0.15 s, forward: 1.48 ± 0.59 s, backward: 1.42 ± 0.37 s), whereas TTSap showed significantly longer times for landings from the forward and backward directions (forward: 4.53 ± 0.17 s, backward: 4.34 0.35 s, medial: 1.18 ± 0.49 s, lateral: 1.11 ± 0.43 s). TTSv showed a significantly shorter time for the forward direction compared with all other landing directions (forward: 2.62 ± 0.31 s, backward: 2.82 ± 0.29 s, medial: 2.91 ± 0.31 s, lateral: 2.86 ± 0.32 s). Based on these results, multiple jump-landing directions should be considered when assessing dynamic stability.

The effect of jump-landing directions on dynamic stability.

The purpose of this study was to investigate the effects of asymmetrical loading on the intersegmental dynamics of the swing phase. Participants were asked to walk on a treadmill for 20min under three loading conditions: (a) unloaded baseline, (b) 2kg attached to the dominant limb's ankle, and (c) post-load, following load removal. Sagittal plane motion data of both legs were collected and an intersegmental dynamics analysis of each swing phase was performed. Comparisons of steady-state responses across load conditions showed that absolute angular impulses of the loaded limb's hip and knee increased significantly after load addition, and returned to baseline following load removal. Unloaded leg steady-state responses were not different across load conditions. However, after a change in leg inertia both legs experienced a period of adaptation that lasted approximately 40 strides before a steady state walking pattern was achieved. These findings suggest that the central nervous system refined the joint moments over time to account for the altered limb inertia and to maintain the underlying kinematic walking pattern. Maintaining a similar kinematic walking pattern resulted in altered moment profiles of the loaded leg, but similar moment profiles of the unloaded leg compared with the unloaded baseline condition.

Gary D. Heise

School of Sport & Exercise Science

University of Northern Colorado

Oscillation and Reaction Board Techniques for Estimating Inertial Properties of a Below-knee Prosthesis

Gary D. Heise

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University of Northern Colorado

Oscillation and Reaction Board Techniques for Estimating Inertial Properties of a Below-knee Prosthesis

School of Sport & Exercise Science