Gradient Walking Research Articles

Biomechanical responses on specific load carriage and positive gradient walking: A pilot study

Objectives: Normal load carriage is an inevitable part of military marching tasks. Military tasks are inextricably related to carrying huge loads irrespective of different terrain. Continuous carrying of heavy loads from level ground to uphill gradient may alter kinetic and kinematic responses. Such responses, in the long run, may cause the risk of injury. This study was designed to find out the effects of external load on kinetic and kinematic responses at specific loads and grades (+10°). Materials and Methods: Six healthy Indian soldiers mean (± standard error of mean [SEM]) age 30.5 ± 3.5 years, height 168.7 ± 2.8 cm, weight 73.8 ± 7.08 kg participated in this study, walking on treadmill (Deneb and Polak-speed-1625) at 3.5 kmph for 6 min at 10° inclination for two conditions, with no-load and 30 kg compact-load at controlled laboratory condition 25°C and 50% relative humidity (RH). Compressive, shearing, torque, joint reaction force, and erector-spine forces for kinetic and angular changes of neck, trunk, thigh, forearm, upper arm, and leg were analysed by biomechanical analysis software (Ergomaster 4.6). A paired t-test and repeated measures analysis of variance were applied to determine the significant effects of the load on dependent variables. Results: Significant changes were found in kinetic (compressive, shearing, torque, joint reactive force, and erector spine force) and kinematic (neck and trunk) parameters with subsequent increments of loads. Conclusion: From this study, it was concluded that walking in uphill condition, compressive, shearing, torque, joint reactive force, and erector spine force was found to be increased by 2.58, 4.65, 4.06, 2.83, and 4.06 folds, the angular changes found in neck and trunk were 1.78 and 1.25 folds compared to no-load conditions, respectively. The exerted forces, namely compressive force 74.12%, shearing force 86%, joint reaction force almost 75%, and erector spine force 83.82%, were very close to the injury risk profile; only the change of torque was not much closer to the risk profile. Such findings could be used for recommending load carriage guidelines for future studies.

Gait and neuromuscular dynamics during level and uphill walking carrying military loads

ABSTRACT The neuromuscular system responds to perturbation and increasing locomotor task difficulty by altering the stability of neuromuscular output signals. The purpose of this study was to determine the effects of two different military load carriage systems on the dynamic stability of gait and muscle activation signals. 14 army office cadets (20 ± 1 years) performed 4-minute treadmill walking trials on level (0%) and uphill (10%) gradients while unloaded, and with 11 kg backpack and 11 kg webbing loads while the activity of 6 leg and trunk muscles and the motion of the centre of mass (COM) were recorded. Loaded and uphill walking decreased stability and increased magnitude of muscle activations compared to loaded and level gradient walking. Backpack loads increased the medio-lateral stability of COM and uphill walking decreased stability of vertical COM motion and increased stride time variability. However, there was no difference between the two load carriage systems for any variable. The reduced stability of muscle activations in loaded and uphill conditions indicates an impaired ability of the neuromuscular control systems to accommodate perturbations in these conditions which may have implications on the operational performance of military personnel. However, improved medio-lateral stability in backpack conditions may indicate that participants were able to compensate for the loads used in this study, despite the decreased vertical stability and increased stride time variability evident in uphill walking. This study did not find differences between load carriage systems however, specific load carriage system effects may be elicited by greater load carriage masses.

Effects of Assistance During Early Stance Phase Using a Robotic Knee Orthosis on Energetics, Muscle Activity, and Joint Mechanics During Incline and Decline Walking.

The knee joint performs a significant amount of positive or negative mechanical work during gradient walking, and targeted assistance during periods of high mechanical work could yield strong human augmentation benefits. This paper explores the biomechanical effects of providing knee extension assistance during the early stance phase of the gait cycle using a powered unilateral knee exoskeleton during gradient walking on able-bodied subjects. Twelve subjects walked on 15% gradient incline and decline surfaces with the exoskeleton providing knee extension assistance during the early stance phase of the gait cycle. For both incline and decline walking, the exoskeleton assistance reduced the muscle activation of the knee extensors on the assisted leg ( ). However, only approximately half the individuals responded to exoskeleton assistance positively by reducing their metabolic cost of walking for both incline and decline tasks. The results indicate that, unlike the individuals who did respond, the individuals who did not respond to the assistance may have penalized their metabolic cost by their biomechanical compensatory behaviors from the unassisted leg.

Predicting Energy Expenditure During Gradient Walking With a Foot Monitoring Device: Model-Based Approach.

BackgroundMany recent commercial devices aim at providing a practical way to measure energy expenditure. However, those devices are limited in accuracy.ObjectiveThis study aimed to build a model of energy consumption during walking applicable to a range of sloped surfaces, used in conjunction with a simple, wearable device.MethodsWe constructed a model of energy consumption during gradient walking by using arguments based in mechanics. We built a foot monitoring system that used pressure sensors on the foot insoles. We did experiments in which participants walked on a treadmill wearing the foot monitoring system, and indirect calorimetry was used for validation. We found the parameters of the model by fitting to the data.ResultsWhen walking at 1.5 m/s, we found that the model predicted a calorie consumption rate of 5.54 kcal/min for a woman with average height and weight and 6.89 kcal/min for an average man. With the obtained parameters, the model predicted the data with a root-mean-square deviation of 0.96 kcal/min and median percent error of 12.4%.ConclusionsOur model was found to be an accurate predictor of energy consumption when walking on a range of slopes. The model uses few variables; thus, it can be used in conjunction with a convenient wearable device.

Parametric Modeling of Human Gradient Walking for Predicting Minimum Energy Expenditure.

A mathematical model to predict the optimum gradient for a minimum energetic cost is proposed, based on previous results that showed a minimum energetic cost when gradient is −10%. The model focuses on the variation in mechanical energy during gradient walking. It is shown that kinetic energy plays a marginal role in low speed gradient walking. Therefore, the model considers only potential energy. A mathematical parameter that depends on step length was introduced, showing that the optimal gradient is a function of that parameter. Consequently, the optimal negative gradient depends on the individual step length. The model explains why recent results do not suggest a single optimal gradient but rather a range around −10%.

Obesity does not impair walking economy across a range of speeds and grades

Despite the popularity of walking as a form of physical activity for obese individuals, relatively little is known about how obesity affects the metabolic rate, economy, and underlying mechanical energetics of walking across a range of speeds and grades. The purpose of this study was to quantify metabolic rate, stride kinematics, and external mechanical work during level and gradient walking in obese and nonobese adults. Thirty-two obese [18 women, mass = 102.1 (15.6) kg, BMI = 33.9 (3.6) kg/m(2); mean (SD)] and 19 nonobese [10 women, mass = 64.4 (10.6) kg, BMI = 21.6 (2.0) kg/m(2)] volunteers participated in this study. We measured oxygen consumption, ground reaction forces, and lower extremity kinematics while subjects walked on a dual-belt force-measuring treadmill at 11 speeds/grades (0.50-1.75 m/s, -3° to +9°). We calculated metabolic rate, stride kinematics, and external work. Net metabolic rate (Ė net/kg, W/kg) increased with speed or grade across all individuals. Surprisingly and in contrast with previous studies, Ė net/kg was 0-6% less in obese compared with nonobese adults (P = 0.013). External work, although a primary determinant of Ė net/kg, was not affected by obesity across the range of speeds/grades used in this study. We also developed new prediction equations to estimate oxygen consumption and Ė net/kg and found that Ė net/kg was positively related to relative leg mass and step width and negatively related to double support duration. These results suggest that obesity does not impair walking economy across a range of walking speeds and grades.

Numerical Methods and Applications in Biomechanical Modeling

Numerical Methods and Applications in Biomechanical Modeling

The Effects of Obesity on the Biomechanics of Gradient Walking

Walking is a popular form of exercise for the prevention and treatment of obesity. However, walking may be a source of biomechanical loads that link obesity and musculoskeletal injury and pathology. During level walking, obese adults may adopt a more erect gait pattern (less knee flexion during stance) that reduces lower extremity net muscle moments (NMM, Nm/kg) compared to non-obese individuals. Walking uphill requires greater hip and knee NMM, but the effects of obesity on the biomechanics of uphill walking are not known. PURPOSE: To quantify the biomechanics of level and gradient walking in obese and non-obese adults. METHODS: Twelve obese, 100.5 (15.7) kg, 33.4 (2.4) kg/m2, (mean (SD)) and eleven non-obese, 68.3 (11.5) kg, 22.0 (2.0) kg/m2 adult volunteers participated in this study. We measured ground reaction forces and three-dimensional lower extremity kinematics while subjects walked on a dual-belt force measuring treadmill at 1.25 m/s with the treadmill grade set at -3, 0, 3, 6 and 9°. We calculated NMM at the hip, knee and ankle. RESULTS: During uphill vs. level walking, all participants walked with greater hip and knee flexion and ankle dorsiflexion during early-mid stance. Peak hip flexion (heel strike) was greater in the obese vs. non-obese when walking up the steeper grades (55 vs. 45° at 6° and 57 vs. 39° at 9°, respectively). Compared to level walking, knee joint range of motion during early stance increased during downhill and decreased during uphill walking, with no differences between the groups. Absolute early-stance hip and knee extensor NMM were greater in obese individuals and increased when walking uphill vs. level walking. Peak early-stance hip extensor NMM in the obese and non-obese adults were 0.78 vs. 0.88 Nm/kg, respectively, during level walking and increased to 1.24 vs. 1.19 Nm/kg, respectively, while walking up the 9° incline. Peak early-stance knee extensor NMM in the obese and non-obese adults were 0.3 vs. 0.37 Nm/kg, respectively, during level walking and increased to 0.71 vs. 0.54 Nm/kg, respectively, while walking up the 9° incline. CONCLUSIONS: While obese adults may be able to walk on level ground with relatively small joint loads, our results suggest that their joint loads increase disproportionally compared to non-obese adults when they walk uphill.

Acceleration versus heart rate for estimating energy expenditure and speed during locomotion in animals: Tests with an easy model species, Homo sapiens

An important element in the measurement of energy budgets of free-living animals is the estimation of energy costs during locomotion. Using humans as a particularly tractable model species, we conducted treadmill experiments to test the validity of tri-axial accelerometry loggers, designed for use with animals in the field, to estimate rate of oxygen consumption ( V ˙ O 2 : an indirect measure of metabolic rate) and speed during locomotion. The predictive power of overall dynamic body acceleration (ODBA) obtained from loggers attached to different parts of the body was compared to that of heart rate ( f H). When subject identity was included in the statistical analysis, ODBA was a good, though slightly poorer, predictor of V ˙ O 2 and speed during locomotion on the flat (mean of two-part regressions: R 2=0.91 and 0.91, from a logger placed on the neck) and V ˙ O 2 during gradient walking (single regression: R 2=0.77 from a logger placed on the upper back) than was f H ( R 2=0.96, 0.94, 0.86, respectively). For locomotion on the flat, ODBA was still a good predictor when subject identity was replaced by subject mass and height (morphometrics typically obtainable from animals in the field; R 2=0.92 and 0.89) and a slightly better overall predictor than f H ( R 2=0.92 and 0.85). For gradient walking, ODBA predicted V ˙ O 2 more accurately than before ( R 2=0.83) and considerably better than did f H ( R 2=0.77). ODBA and f H combined were the most powerful predictor of V ˙ O 2 and speed during locomotion. However, ODBA alone appears to be a good predictor and suitable for use in the field in particular, given that accelerometry traces also provide information on the timing, frequency and duration of locomotion events, and also the gait being used.

Ergonomic effects of load carriage on energy cost of gradient walking

We examined the effects of load on the energy cost of walking ( C w), being defined as the ratio of the 2-min steady-state oxygen consumption to the speed, and economical speed (ES) during level and gradient walking. Ten men walked on a treadmill at various speeds with and without a load on their back at 0% and ±5% gradients. Significantly lower C w values were observed only when the load was carried on the back during level walking at slower speeds. The ES was significantly decreased by less than 5% when the load was carried on the back. Significant gradient differences were also observed in the ES in the load and no load conditions. These results would be applicable to a wider range of occupational and leisure tasks.

Himalayan porter's specialization: metabolic power, economy, efficiency and skill.

Carrying heavy loads in the Himalayan region is a real challenge. Porters face extreme ranges in terrain condition, path steepness, altitude hypoxia and climate for 6-8h a day, many months a year, since they were boys. It has been previously shown that, when carrying loads on level terrain, porters' metabolic economy is higher than in Caucasians but the reasons are still unknown. We monitored Nepalese porters both during 90 km trekking in Khumbu Valley and at two different altitudes (3490 and 5050 m above sea-level), where they were compared to Caucasian mountaineers during (22%) gradient walking. Both subject groups carried a load of up to 90% body mass. The remarkably higher performance of porters during uphill locomotion (+60% in speed, +39% mechanical power) is only partly explained by the lower cost of loaded walking (-20%), being also the result of a better cardio-circulatory adaptation to altitude, which generates a higher mass-specific metabolic power (+30%). Consequently, Nepalese porters show higher efficiency, both during uphill and downhill loaded walking. Their higher economy on steep paths cannot be ascribed to a better exchange between potential and kinetic energy, as in our experiments the body centre of mass travelled monotonically uphill (or downhill). A different oscillation pattern of the loaded head-trunk segment, together with the analysis of the different components of the mechanical work during load carrying, suggests that achieved motor skills in balancing the loaded body segment above the hip could play a role in determining the better economy of porters.

Mechanical determinants of gradient walking energetics in man.

1. The metabolic cost and the mechanical work at different speeds during uphill, level and downhill walking have been measured in four subjects. 2. The mechanical work has been partitioned into the internal work (W(int)), due to the speed changes of body segment with respect to the body centre of mass (BCM), and the external work (W(ext)), related to the position and speed changes of the BCM in the environment. 3. W(ext) has been further divided into a positive part W+ext) and a negative one (W-(ext)), associated with the energy increases and decreases, respectively, over the stride period. 4. For all constant speeds the most economical gradient has been found to be -10.2% (+/- 0.8 S.D.). 5. At each gradient there is a unique W+ext/W-ext ratio (= 1 in level walking), regardless of speed, with a tendency for W-ext and W+ext to vanish above +15% and below -15% gradient, respectively. 6. W(int) is constant at each speed regardless of gradient. This is partly explained by an only slight decrease in stride frequency at increasing gradient. W(int) constancy implies that it has no role in determining the optimum gradient. 7. A linear multiple regression relating W+ext and W-ext to the metabolic cost at different gradients showed that negative (eff-) and positive (eff+) efficiencies decrease with increasing speed (from 0.912 to 0.726, and from 0.182 to 0.146, respectively). The eff-/eff+ ratio, however, remains rather constant (4.995 +/- 0.125 S.D.). 8. We conclude that the measured W(ext), the W+ext/W-ext partitioning and eff-/eff+ ratio, i.e. the different efficiency of the muscles used as force and brake generators, can explain the metabolic optimum gradient at about -10%.

An equation for prediction of energy expenditure of walking and running.

An equation for prediction of energy expenditure of walking and running.