Unloaded Walking Research Articles

Transverse plane kinetics during treadmill walking with and without a load

Objective. The purpose of this experiment was to determine the effects of wearing a backpack on transverse plane upper and lower body torque. Background. During unloaded walking the upper and lower body counter-rotate to reduce the net angular momentum of the body. There is less counter-rotation while carrying a load, suggesting a more rigid link between the upper and lower body. We predicted that load carriage would result in an increase in upper body torque. Because the upper and lower body may be more rigidly linked during load carriage, we also predicted an increase in lower body torque. Methods. Twelve subjects (5 male, 7 female, mean age=26) walked with and without a backpack containing 40% of their body mass on a treadmill at speeds from 0.6 to 1.6 m s −1 . Kinematic data were sampled for 30 s at each speed, upper and lower body torque were calculated from angular acceleration and moment of inertia. Results. Higher levels of upper and lower body torque were observed during load carriage than during unloaded walking. However, the increase in upper body torque was 225%, while upper body moment of inertia increased by 400%. Conclusions. The differences in torque between loaded and unloaded walking suggest that a goal of loaded walking is to minimize upper body torque, which may reduce the likelihood of injury. Relevance Knowledge of the effects of load carriage on upper and lower body torque, and related changes in coordination may provide insight into injury reduction mechanisms during load carriage.

Muscular and metabolic costs of uphill backpacking: are hiking poles beneficial?

The purpose of the present study was to compare pole and no-pole conditions during uphill backpacking, which was simulated on an inclined treadmill with a moderately heavy (22.4 kg, 30% body mass) backpack. Physiological measurements of oxygen consumption, heart rate, and RPE were taken during 1 h of backpacking in each condition, along with joint kinematic and electromyographic comparisons from data collected during a third test session. The results showed that although imposing no metabolic consequence, pole use elicited a longer stride length (1.27 vs 1.19 m), kinematics that were more similar to those of unloaded walking, and reduced activity in several lower extremity muscles. Although pole use evoked a greater heart rate (113.5 vs 107 bpm), subjects were backpacking more comfortably as indicated by their ratings of perceived exertion (10.8 vs 11.6). The increased cardiovascular demand was likely to support the greater muscular activity in the upper extremity, as was observed in triceps brachii. By redistributing some of the backpack effort, pole use alleviated some stress from the lower extremities and allowed a partial reversal of typical load-bearing strategies.

Kinetic changes associated with load carriage using two rucksack designs

This study assessed changes in kinetics from unloaded walking associated with load carriage using both a traditional and a new rucksack design that incorporates front balance pockets (AARN). Nine subjects walked at 3(±0.05) km.h-1 over a force plate unloaded and carrying 25.6 kg in each of the rucksacks. The order of trials was randomized and speed-controlled by use of photoelectric cells and a millisecond timer. Anteroposterior and vertical ground reaction forces were analyzed using repeated measures ANCOVA (speed covariate). There was a trend for the AARN pack to elicit a shorter support time than the traditional pack, 1.025±0.049 versus 1.037±0.06 s (p = 0.056), while the unloaded condition produced the shortest support time, 1.016±0.04 s. Both braking and propulsive forces for the rucksacks were significantly greater than for unloaded walking. While there was no significant difference between the packs for the braking force, the AARN pack produced a significantly lower (p < 0.05) propulsive force than the traditional rucksack, 0.79±0.2 versus 0.94±0.16 N.kg bodyweight-1. Both rucksacks produced significantly greater (p < 0.001) vertical force peaks than unloaded walking, the increases being proportional to the increase in system weight. These findings indicate that there may be some advantage in terms of propulsive force production for the front/back system.

The oxygen consumption associated with unloaded walking and load carriage using two different backpack designs.

The purpose of this study was to assess the energy expenditure associated with load carriage using both a traditional rucksack and a new rucksack design, the AARN rucksack, which incorporates front balance pockets. Nine volunteers walked at 3 km h(-1) at various uphill and downhill gradients on a treadmill without a load and carrying a load of 25.6 kg in each of the rucksacks. The oxygen consumption associated with both of the loading conditions was significantly (P < 0.001) higher than that associated with unloaded walking at all downhill gradients tested, although there was no significant difference between the two loading conditions. During the uphill gradients the oxygen consumption associated with the AARN pack was significantly (P < 0.05) lower than that associated with the traditional pack at the 0%, 5%, 10% and 20% gradients. The mean (%) differences at these gradients, expressed in ml x kg(-1) x min(-1) were 1.18 (9%), 1.45 (8%), 1.76 (8%) and 1.88 (6%), respectively. On average for the whole protocol, the oxygen consumption associated with the AARN rucksack was 5% lower than that associated with the traditional rucksack [mean (SD) 17.28 (7.46) ml x kg(-1) x min(-1) for the AARN pack and 18.20 (7.84) ml x kg(-1) x min(-1) for the traditional pack]. The findings of the present study suggest that a load carriage system that allows the load to be distributed between the back and font of the trunk is more appropriate for carrying relatively heavy loads than a system that loads the back only.

Physiological and biomechanical responses during treadmill walking with graded loads.

Eleven healthy men [mean (SD) for age, height, body mass and maximum oxygen consumption: 25.1 (3.0) years, 1.79 (0.06) m, 78.2 (10.5) kg and 56.9 (7.1) ml x kg(-1) x min(-1), respectively) completed two treadmill walking tests at their self-selected velocity while bilaterally carrying 15-kg and 20-kg loads (in a boxed container) for 4 min in front of the body. Each handle of the boxed container was fitted with a load cell so as to allow quantification of the load supported by each hand during load carriage. During the tests, oxygen uptake (VO2), heart rate (HR), and blood pressure (BP) were monitored using standardized procedures, and cardiac output (Qc) was measured using the carbon dioxide rebreathing method. Stroke volume (SV), arterio-venous oxygen difference (C(a-v)O2), rate pressure product (RPP) and total peripheral resistance (TPR) were calculated from the above measurements. The results showed that the two extremities sustained approximately 60% to 70% of the total load, with the balance being supported by the body. Significant increases (P < 0.05) in VO2, HR, Qc, and mean BP were observed during both of the load carriage walks compared to unloaded walking. However, SV, C(a-v)O2, RPP and TPR were unchanged (P > 0.05) during load carriage. Although VO2 was significantly higher during the 20-kg load carriage walk, no significant differences were observed between the two loads for any of the cardiovascular responses monitored. Contrary to our hypothesis, these results suggest that increasing the load from 15 kg to 20 kg during treadmill walking does not significantly increase the cardiovascular stress that occurs in healthy subjects.

Bone-on-Bone Forces during Loaded and Unloaded Walking

Joint moments and bone-on-bone forces in the ankle, knee and hip joint were studied in 7 healthy male subjects during unloaded and loaded walking. The subjects walked across a force platform while they were filmed at 200 Hz. Loaded walking was examined at 10 and 20 kg load carried symmetrically in the hands. Peak joint moments and peak bone-on-bone forces increased from unloaded to loaded walking for the ankle and hip joint (p < 0.05). The lowest bone-on-bone forces were found at the ankle joint (3,318 +/- 390 N) during unloaded walking and the highest at the hip joint (6,399 +/- 1,517 N) during 20 kg loading. Expressed relative to body weight (BW) these values corresponded to 4.2 +/- 0.50 and 8.0 +/- 1.78 BW). However, the individual values showed that 2 of the 7 subjects differed remarkably from the other 5, especially with respect to the hip joint loadings. During loaded walking (20 kg) these 2 subjects showed 14.4 and 15.1 BW peak compression force in the hip joint while the remaining subjects were all below 6.3 BW, which could be explained by the 2 subjects' low ankle joint moments and higher knee and hip joint moments. Apparently, a total 'leg moment' formed by the three major joints is required to support the body and maintain the locomotion, although the relative contribution from each joint can differ among individuals. The peak joint moments were the most dominant contributor to the peak bone-on-bone forces. Therefore, it is concluded that interindividual differences in walking style can lead to pronounced differences in peak bone-on-bone forces. It remains unclear how these interindividual differences are related to joint degradation.

Energy cost of backpacking in heavy boots.

Previous studies have investigated the oxygen cost ([Vdot]02) of increasing boot weight during unloaded walking or running, and have shown that for each 100 g increase in weight of footwear there is a 0·7-1·0% increase in [Vdot]O2 In reality (except in athletic events) the use of heavy footwear is associated with load carriage, usually backpacking. We therefore investigated the effects of increasing boot weight by 5% of body weight on the [Vdot]02 of backpacking a load amounting to 35% of the body-weight in five healthy young males who walked at 4·5 km/hour (0% grade) on a motor-driven treadmill. The results indicated a mean increase of 0·96% in [Vdot]02 whilst backpacking for each 100thinsp;-g increase in boot weight. In contrast the oxygen cost of increasing the backpack load was only 0·15% indicating that it was 6·4 times more expensive to carry weight on the feet as compared to the back. It is concluded that the relation between boot weight and oxygen cost, previously developed for unloaded walking and running, can reasonably be extended to include heavier boots and backpacking.

Muscular efficiency during steady-rate exercise. II. Effects of walking speed and work rate.

A comparison of walking against vertical (gradient) and horizontal (trailing weight) forces was made during steady-rate exercise at 0.250, 500, and 750 kg-m/min with speeds of 3,0, 4.5, and 6.0 km/h. In all cases exponential relationships between energy expenditure (calculated from the steady-rate respiration) and increasing work rate and speed were observed which indicated that muscular efficiency during walking is inversely related to speed and work rate. "Work" (level, unloaded walking as the baseline correction), "delta" (measured work rate as the baseline correction), and "instantaneous" (derived from the equation describing the caloric cost of work) efficiencies were computed. All definitions yielded decreasing efficiencies with increasing work rates. At work rates above 250 kg-m/min the curves describing the relationship between energy expenditure and work rate were parallel for vertical and horizontal forces, indicating equivalent efficiencies in this range. Only the delta and instantaneous definitions accurately described these relationships for vertical and horizontal work. Determinations of combined work loads (gradient plus trailing weight) were made and the energy costs of both types of work found to be additive.