Jeremy D. Smith

Effects of load carriage and footwear on spatiotemporal parameters, kinematics, and metabolic cost of walking

Gait patterns are commonly altered when walking or running barefoot compared to shod conditions. Although controversy exists as to whether barefoot conditions result in lower metabolic costs, it is clear that adding load to the body results in increased metabolic costs. The effects of footwear and backpack loading have been investigated separately, but it is unclear whether manipulating both simultaneously would cause similar outcomes. Twelve healthy individuals (7 female, 5 male) with no obvious gait abnormalities participated in this study (age=24±2 years, height=1.73±0.13 m, and mass=71.1±16.9 kg). Steady state metabolic data and 3D motion capture were collected during treadmill walking at 1.5 ms(-1) in four conditions: Barefoot Unloaded, Shod Unloaded, Barefoot Loaded, and Shod Loaded. Barefoot walking elicited shorter stride lengths, stance and double support times, as well as a slight (≈1%), but not significant, decrease in metabolic cost. Loading increased metabolic costs of walking but did not elicit spatiotemporal changes in either footwear condition. Lower limb kinematic differences were noted in response to both loading and footwear. Changes in spatiotemporal parameters observed when walking barefoot were not exacerbated by the addition of a backpack load. This suggests that the increased metabolic demand associated with the load is met with a similar spatiotemporal pattern whether a person wears a supportive shoe or not. Thus, the discomfort associated with foot strike while barefoot that promotes spatiotemporal changes seems to be independent of load.

Short and Longer Term Changes in Amputee Walking Patterns Due to Increased Prosthesis Inertia

The purpose of this study was to quantify the time course of changes in walking patterns among unilateral, transtibial amputees whose prosthesis inertia properties were substantially altered to match with those of their intact limb. Four unilateral transtibial amputees completed three test sessions on days 1, 2, and 8 of an 8-day protocol. Walking kinetics were computed from overground trials; temporal characteristics were collected during treadmill walking. Assessments were initially performed on day 1 without additional mass on the prosthesis. Mass was then added to the distal aspect of the prosthesis such that the mass and moment of inertia of the prosthetic leg were matched with those of the intact shank and foot. This added mass remained attached to the prosthetic limb for the next 7 days. Gait assessments were completed immediately and after 5, 10, 15, 30, and 60 minutes of exposure to the altered inertia. Amputees returned to the laboratory on days 2 and 8 for additional assessments. Measures of gait symmetry between the intact and prosthetic legs changed within 5 minutes of exposure to altered prosthesis inertia and remained in this altered state until the load was removed on the eighth day, at which time symmetry indices returned to their original state. Matching the inertia properties between legs exacerbated stance time and swing time asymmetries but improved peak knee moment symmetry during swing termination. The increased joint kinetic symmetry, however, required greater muscular efforts, particularly on the prosthetic side. In conclusion, substantial alteration of the inertia properties of the prosthesis immediately altered temporal and joint kinetic symmetry between intact and prosthetic legs, both when mass was added to the prosthesis and when that mass was removed. Because of our small sample size, caution should be exercised when generalizing these outcomes to all lower limb amputees.

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.

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.

Effects of load carriage and footwear on lower extremity kinetics and kinematics during overground walking.

Kinetic and kinematic responses during walking vary by footwear condition. Load carriage also influences gait patterns, but it is unclear how an external load influences barefoot walking. Twelve healthy adults (5 women, 7 men) with no known gait abnormalities participated in this study (age=23±3years, height=1.73±0.11m, and mass=70.90±12.67kg). Ground reaction forces and 3D motion were simultaneously collected during overground walking at 1.5ms-1 in four conditions: Barefoot Unloaded, Shod Unloaded, Barefoot Loaded, and Shod Loaded. Barefoot walking reduced knee and hip joint ranges of motion, as well as stride length, stance time, swing time, and double support time. Load carriage increased stance and double support times. The 15% body weight load increased GRFs ∼15%. Walking barefoot reduced peak anteroposterior GRFs but not peak vertical GRFs. Load carriage increased hip, knee, and ankle joint moments and powers, while walking barefoot increased knee and hip moments and powers. Thus, spatiotemporal and kinematic adjustments to walking barefoot decrease GRFs but increase knee and hip kinetic measures during overground walking. The ankle seems to be less affected by these footwear conditions. Regardless of footwear, loading requires larger GRFs, joint loads, and joint powers.

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.

Asymmetrical loading affects intersegmental dynamics during the swing phase of walking

Much of the work related to lower extremity inertia manipulations has focused on temporal, kinematic and traditional inverse dynamics assessments during locomotion. Intersegmental dynamics is an analytical technique that provides further insights into mechanisms underlying linked-segment motion. The purpose of this study was to determine how intersegmental dynamics during the swing phase of walking are altered during asymmetrical lower extremity loading. Participants walked overground at a speed of 1.57 ms(-1) with 0, 0.5, 1.0, and 2.0 kg attached to one foot. Net, interaction, gravitational, and muscle moments were computed. Moment magnitudes at joints of the loaded leg increased systematically with increasing load, whereas unloaded leg moments were unaffected by loading. With increasing load, relative contributions of interaction moments about the knee and hip and gravitational moment about the ankle increased (i.e., 21%, 8%, and 44% increases, respectively), whereas the relative contributions of muscle moments about all three joints declined (i.e., -4%, -13%, and -8% decreases for the ankle, knee, and hip, respectively for unloaded vs. 2.0 kg). These results suggest that altered inertia properties of the limb not only affected the amount of muscular effort required to swing the leg, but also changed the nature of the interaction between segments.

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.

Performance and Health Related Characteristics of Male Athletes Using Marijuana.

Lisano, JK, Smith, JD, Mathias, AB, Christensen, M, Smoak, P, Phillips, KT, Quinn, CJ, and Stewart, LK. Performance and health-related characteristics of physically active men using marijuana. J Strength Cond Res 33(6): 1659-1669, 2019-The influence of chronic marijuana use on the performance and health of physically active individuals has yet to be fully elucidated. The purpose of this study was to explore pulmonary function, aerobic and anaerobic fitness, strength, serum testosterone, cortisol, C-reactive protein (CRP), Δ-9-tetrahydrocannabinol (THC), 11-nor-9-carboxy-Δ-9-tetrahydrocannabinol (THC-COOH), and 11-hydroxy-Δ-9-tetrahydrocannabinol (THC-OH) concentrations in a physically active population either using or not using marijuana. Healthy, physically active males (N = 24) were compared based on their marijuana-use status: marijuana users (MU; n = 12) and nonusers (NU; n = 12). Statistical analysis (p = 0.05) revealed no difference between groups for age, body mass, body mass index, body fat, forced expiratory volume in 1 second percentage, VO2max, anaerobic power output, strength measures, testosterone, or cortisol concentrations. Although not statistically significant, MU showed a trend to fatigue to a greater percentage of absolute power output than NU from the beginning to the end of the Wingate Anaerobic Power Assessment (p = 0.08, effect size = 0.75). C-reactive protein in MU (1.76 ± 2.81 mg·L) and NU (0.86 ± 1.49 mg·L) was not significantly different (p = 0.60) but placed MU at moderate risk and NU at low risk for cardiovascular disease. Anaerobic fatigue was the only performance variable to show a trend for difference between groups. These results suggest that marijuana use in physically active males may not have significant effects on performance; however, it may be linked to elevated concentrations of CRP which place users at a higher risk for cardiovascular disease.

Ertl and Non-Ertl amputees exhibit functional biomechanical differences during the sit-to-stand task

Background People with transtibial amputation stand ˜ 50 times/day. There are two general approaches to transtibial amputation: 1) distal tibia and fibula union using a “bone‐bridge” (Ertl), 2) non‐union of the tibia and fibula (Non‐Ertl). The Ertl technique may improve functional outcomes by increasing the end‐bearing ability of the residual limb. We hypothesized individuals with an Ertl would perform a five‐time sit‐to‐stand task faster through greater involvement/end‐bearing of the affected limb. Methods Ertl (n = 11) and Non‐Ertl (n = 7) participants sat on a chair with each foot on separate force plates and performed the five‐time sit‐to‐stand task. A symmetry index (intact vs affected limbs) was calculated using peak ground reaction forces. Findings The Ertl group performed the task significantly faster (9.33 s (2.66) vs 13.27 (2.83) s). Symmetry index (23.33 (23.83)% Ertl, 36.53 (13.51)% Non‐Ertl) indicated the intact limb for both groups produced more force than the affected limb. Ertl affected limb peak ground reaction forces were significantly larger than the Non‐Ertl affected limb. Peak knee power and net work of the affected limb were smaller than their respective intact limb for both groups. The Ertl intact limb produced significantly greater peak knee power and net work than the Non‐Ertl intact knee. Interpretation Although loading asymmetries existed between the intact and affected limb of both groups, the Ertl group performed the task ˜ 30% faster. This was driven by greater power and work production of the Ertl intact limb knee. Our results suggest that functional differences exist between the procedures. HighlightsFunctional differences between Ertl and Non‐Ertl amputations are unknown.The Ertl group performed the sit‐to‐stand task ˜ 30% faster.Ertl amputated limb peak ground reaction forces were significantly larger.Our results suggest that functional differences exist between the procedures.