Gary D. Heise

“leg spring” characteristics and the aerobic demand of running

PURPOSE By applying a simple, linear mass-spring model to running, the normalized leg spring stiffness (Kleg), the normalized effective vertical stiffness (Kvert), and the mass-specific mechanical power output of the spring (Psp) were determined and correlated with aerobic demand. The purpose of the study was to determine whether leg spring characteristics explain any of the interindividual variability observed in aerobic demand at a given submaximal running speed. METHODS Recreational runners (N = 16) ran on a treadmill at 3.35 m x s(-1) for physiological measures and overground for biomechanical measures. The latter included a sagittal plane video record of the running motion and ground reaction data. RESULTS We found no relationship between the aerobic demand of running and Kleg (r = -0.18), an inverse relationship between aerobic demand and Kvert (r = -0.48), and a positive correlation between aerobic demand and Psp (r = 0.45). CONCLUSIONS The inverse relationship between Kvert and aerobic demand indicates that less economical runners possess a more compliant running style during ground contact. This running style may place greater force demands on extensor musculature.

Interrelationships between mechanical power, energy transfers, and walking and running economy.

The interrelationships between aerobic demand, kinematic and kinetic-based estimates of mechanical power output and energy transfer, and total body angular impulse (summation of net joint moments integrated with respect to time over a stride) were quantified for walking at 1.69 m.s-1 and running at 3.35 m.s-1 to assess the ability of these various biomechanical expressions to explain interin-dividual differences in walking and running economy. Fourteen healthy men participated in the walking study and 16 recreational male runners were subjects for the running analysis. Each subject performed treadmill locomotion for determination of aerobic demand and overground locomotion from which biomechanical measures were quantified. It was expected that mechanical power and angular impulse expressions would correlate positively with aerobic demand while energy transfer expressions would correlate negatively. Correlations between aerobic demand and power estimates primarily were positive, but explained no more than 32% of the variability in walking or running VO2 (center of mass model: 0.22 < r < 0.57; segment-based model: -0.02 < r < 0.20; kinetic model: -0.07 < r < 0.22). Total body angular impulse also correlated positively with aerobic demand (0.32 < r < 0.42). Energy transfer expressions from the various analytical models showed no consistent relationship with aerobic demand, either in terms of magnitude or direction (-0.26 < r < 0.48). It was concluded that mechanical power, energy transfer, and angular impulse expressions frequently used in analyses of gait explain only a small proportion of normal interindividual variability in the aerobic demand at a given speed of walking or running.

The effect of handgrip position on upper extremity neuromuscular responses to arm cranking exercise

The purpose of this study was to determine if handgrip position during arm cranking exercise influences the neuromuscular activity of muscles biceps brachii (BB), lateral head of triceps brachii (TB), middle deltoid (DT), infraspinatus (IS) and brachioradialis (BR). Fifteen participants cranked an arm ergometer using three different handgrip positions (supinated, pronated, and neutral). Electromyographic (EMG) data were recorded from the aforementioned muscles, and relative duration of EMG activation and amplitude were quantified for the first and second 180 degrees of crank angle. EMG measures were analyzed with MANOVA and follow-up univariate procedures; alpha was set at 0.01. The relative durations of EMG activation did not differ between handgrip positions. Muscle IS exhibited 36% less amplitude in the supinated versus neutral handgrip position (second half-cycle), and muscle BR displayed 63% greater amplitude across cycles in the neutral versus supinated and pronated handgrip positions. The greater BR activity displayed in the neutral handgrip position may reflect its anatomical advantage as an elbow flexor when the forearm is in neutral position. Muscle IS exhibited less activity in the supinated position and may be clinically relevant if it allows arm cranking to occur without subsequent shoulder pain, which is often the aim of shoulder rehabilitation.

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

Sato, K and Heise, GD. Influence of weight distribution asymmetry on the biomechanics of a barbell back squat. J Strength Cond Res 26(2): 342–349, 2012—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.

Comparison of Back Squat Kinematics Between Barefoot and Shoe Conditions

The purpose of the study was to compare the kinematics of the barbell back squat between two footwear conditions and to evaluate the results with respect to recommendations put forth in the National Strength and Conditioning Association position statement for proper squat technique. Twenty-five subjects with 5 – 7 years of resistance training experience participated. Selected kinematics were measured during a 60% of 1RM barbell back squat in both barefoot and athletic shoe conditions. Paired-samples T tests were performed to compare the two footwear conditions. Significant differences were found in trunk (50.72±8.27 vs. 46.97±9.87), thigh (20.94±10.19 vs. 24.42±11.11), and shank segment angles (59.47±5.54 vs. 62.75±6.17), and knee joint angles (81.33±13.70 vs. 88.32±15.45) at the peak descent position. Based on the kinematic analysis of the barefoot squat, two kinematic advantages are countered by two disadvantages. Coaches and instructors should acknowledge these results with respect to a performers capability, and be aware the advantages and disadvantages of barefoot squat from a kinematic perspective.

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 prosthesis, and 2) contrast the effects of the proposed technique and that of using intact limb inertial properties on joint kinetic estimates during walking in unilateral, transtibial amputees. An oscillation and reaction board system was validated and shown to be reliable when measuring inertial properties of known geometrical solids. When direct measurements of inertial properties of the prosthesis were used in inverse dynamics modeling of the lower extremity compared with inertial estimates based on an intact shank and foot, joint kinetics at the hip and knee were significantly lower during the swing phase of walking. Differences in joint kinetics during stance, however, were smaller than those observed during swing. Therefore, researchers focusing on the swing phase of walking should consider the impact of prosthesis inertia property estimates on study outcomes. For stance, either one of the two inertial models investigated in our study would likely lead to similar outcomes with an inverse dynamics assessment.

Relative Contributions to the Net Joint Moment for a Planar Multijoint Throwing Skill: Early and Late in Practice

The purpose of this investigation was to determine, for a planar, multijoint throwing skill, if the relative contributions of the components of the net joint moment (NJM) at the elbow and shoulder change after practice. Each participant (N = 7) performed 200 throwing trials equally distributed across 5 consecutive days. Each participant threw a 0.15-kg ball as far as possible using the nondominant arm while the motion of the throwing arm was restrained to a horizontal plans. From video data and body segment inertial estimations, NJMs and NJM components (i.e., generalized muscle moments and motion-dependent moments) were calculated for selected early and late practice trials. Performance (throwing distance) showed an expected improvement from early to late practice. The dynamics analysis indicated that participants increased average NJMs and NJM components at both joints. However, the relative contribution of NJM components, expressed as ratios of those components to the NJM at each joint, did not change after extended practice. Restraining the throwing arm to a horizontal plane may partly explain why no changes were found in the relative contributions of NJM components. The lack of change in moment ratios support a motor strategy of scaling joint moments for faster movements.

Changes in intersegmental dynamics over time due to increased leg inertia

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 limbs 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 limbs 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.

Averaging Trials Versus Averaging Trial Peaks: Impact on Study Outcomes

Gait data are commonly presented as an average of many trials or as an average across participants. Discrete data points (eg, maxima or minima) are identified and used as dependent variables in subsequent statistical analyses. However, the approach used for obtaining average data from multiple trials is inconsistent and unclear in the biomechanics literature. This study compared the statistical outcomes of averaging peaks from multiple trials versus identifying a single peak from an average profile. A series of paired-samples t tests were used to determine whether there were differences in average dependent variables from these 2 methods. Identifying a peak value from the average profile resulted in significantly smaller magnitudes of dependent variables than when peaks from multiple trials were averaged. Disagreement between the 2 methods was due to temporal differences in trial peak locations. Sine curves generated in MATLAB confirmed this misrepresentation of trial peaks in the average profile when a phase shift was introduced. Based on these results, averaging individual trial peaks represents the actual data better than choosing a peak from an average trial profile.

Comparison of posture and balance in cancer survivors and age-matched controls

Background: The combination of peripheral neuropathy and other treatment‐associated side effects is likely related to an increased incidence of falls in cancer survivors. The purpose of this study was to quantify differences in postural stability between healthy age‐matched controls and cancer survivors. Methods: Quiet standing under four conditions (eyes open/closed, rigid/compliant surface) was assessed in 34 cancer survivors (2 males, 32 females; age: 54(13) yrs., height: 1.62(0.07) m; mass: 78.5(19.5) kg) and 34 age‐matched controls (5 males, 29 females; age: 54(15) yrs.; height: 1.62(0.08) m; mass: 72.8(21.1) kg). Center of pressure data were collected for 30 s and the trajectories were analyzed (100 Hz). Three‐factor (group*surface*vision) mixed model MANOVAs with repeated measures were used to determine the effect of vision and surface on postural steadiness between groups. Findings: Cancer survivors exhibited larger mediolateral root‐mean square distance and velocity of the center of pressure, as well as increased 95% confidence ellipse area (P < 0.01) when compared with their age‐matched counterparts. For example, when removing visual input, cancer survivors had an average increase in 95% confidence ellipse area of 91.8 mm2 while standing on a rigid surface compared to a 68.6 mm2 increase for the control group. No frequency‐based center of pressure measures differed between groups. Interpretation: Cancer survivors exhibit decreased postural steadiness when compared with age‐matched controls. For cancer survivors undergoing rehabilitation focused on existing balance deficits, a small subset of the center of pressure measures presented here can be used to track progress throughout the intervention and potentially mitigate fall risk. HighlightsCancer survivors exhibit less postural steadiness than age‐matched controls.Center of pressure based measures change with varied vision and surface conditions.A subset of center of pressure metrics can adequately assess postural stability.Only time‐domain measures found differences between cancer survivors and controls.Time‐domain measures may be more useful when quantifying postural deficits.