External Mechanical Work Research Articles

Influence of ankle-foot orthoses on kinematic segmental covariation among stroke patients

To evaluate the effect of ankle-foot orthosis on lower limbs kinematic segmental covariation (KSC) among stroke patients. Ten chronic hemiparetic spastic stroke patients presenting with a lack of ankle dorsiflexion were assessed with instrumented gait analysis under three conditions: wearing a shoe, with a prefabricated ankle-foot orthosis (AFO), and with a dynamic AFO. Kinematic parameters were recorded and computed KSC was calculated according to Borghese's methodology. Contrary to the prefabricated AFO, the dynamic AFO improved KSC of the paretic side. We observed a high correlation between the external mechanical work and the affected side's KSC. In the unaffected side, KSC was globally unchanged. In stroke patients, wearing a dynamic AFO improves KSC of the paretic lower limb only.

The effect of Q Factor on gross mechanical efficiency and muscular activation in cycling

Unexplored in scientific literature, Q Factor describes the horizontal width between bicycle pedals and determines where the foot is laterally positioned throughout the pedal stroke. The aim of the study was to determine whether changing Q Factor has a beneficial effect upon cycling efficiency and muscular activation. A total of 24 trained cyclists (11 men, 13 women; VO2max 57.5 ml·kg/min ± 6.1) pedaled at 60% of peak power output for 5 min at 90 rpm using Q Factors of 90, 120, 150, and 180 mm. Power output and gas were collected and muscular activity of the gastrocnemius medialis (GM), tibialis anterior (TA), vastus medialis (VM), and vastus lateralis (VL) measured using surface electromyography. There was a significant increase (P < 0.006) in gross mechanical efficiency (GME) for 90 and 120 mm (both 19.38%) compared with 150 and 180 mm (19.09% and 19.05%), representing an increase in external mechanical work performed of approximately 4-5 W (1.5-2.0%) at submaximal power outputs. There was no significant difference in the level of activity or timing of activation of the GM, TA, VM, and VL between Q Factors. Other muscles used in cycling, and possibly an improved application of force during the pedal stroke may play a role in the observed increase in GME with narrower Q Factors.

Energetics and mechanics of running men: the influence of body mass

We investigated the relationship between mechanical and energy cost of transport and body mass in running humans. Ten severely obese (body mass ranging from 108.5 to 172.0kg) and 15 normal-weighted (52.0-89.0kg) boys and men, aged 16.0-45.8years, participated in this study. The rate of O(2) consumption was measured and the subjects were filmed with four cameras for kinematic analysis, while running on a treadmill at 8kmh(-1). Mass specific energy cost (C (r)) and external mechanical work (W (ext)) per unit distance were calculated and expressed in joules per kilogram per meter, efficiency (η) was then calculated as W (ext)×C (r) (-1) ×100. Both mass-specific C (r) and W (ext) were found to be independent of body mass (M) (C (r)=0.002M+3.729, n=25, R (2)=0.05; W (ext)=-0.001M+1.963, n=25, R (2)=0.01). It necessarily follows that the efficiency is also independent of M (η=-0.062M+53.3298, n=25, R (2)=0.05). The results strongly suggest that the elastic tissues of obese subjects can adapt (e.g., thickening) to the increased mass of the body thus maintaining their ability to store elastic energy, at least at 8kmh(-1) speed, at the same level as the normal-weighted subjects.

Hydrated-ion ordering in electrical double layers

In this work we revisit the surface forces measured between two atomically flat mica surfaces submerged in a reservoir of potassium nitrate (KNO(3)) solution. We consider a comprehensive range of concentrations from 0.08 mM to 2.6 M. The significantly improved resolution available from the extended surface force apparatus (eSFA) allows the distinction of hydration structures and hydrated-ion correlations. Above concentrations of 0.3 mM, hydrated-ion correlations give rise to multiple collective transitions (4 ± 1 Å) in the electrical double layers upon interpenetration. These features are interpreted as the result of hydrated-ion ordering (e.g. layering), in contrast to the traditional interpretation invoking water layering. The hydrated-ion layer adjacent to the surface (i.e. outer Helmholtz layer) is particularly well defined and plays a distinctive role. It can be either collectively expelled in a 5.8 ± 0.3 Å film-thickness transition or collectively forced to associate with the surface by external mechanical work. The latter is observed as a characteristic 2.9 ± 0.3 Å film-thickness transition along with an abrupt decrease of surface adhesion at concentrations above 1 mM. At concentrations as low as 20 mM, attractive surface forces are measured in deviation to the DLVO theory. The hydration number in the confined electrolyte seems to be significantly below that of the bulk. A 1-3 nm thick ionic layer solidifies at the surfaces at concentrations >100 mM, i.e. below bulk saturation.

Biomechanical Evaluation of an Innovative Spring-Loaded Axillary Crutch Design

ABSTRACT We evaluated an innovative spring-loaded crutch design by comparing its performance with standard crutches through a biomechanical approach. Gait analysis was conducted for 7 male subjects under two conditions: walking with standard crutches and with spring-loaded crutches. Three-dimensional kinematic data and ground reaction force were recorded. Spatiotemporal variables, external mechanical work, and elastic energy (for spring crutches) were calculated based on recorded data. The trajectories of vertical ground reaction forces with standard crutches had two main peaks before and after mid-stance, and those with optimized spring-loaded crutches had only one main peak. The magnitude of external mechanical work was significantly higher with spring-loaded crutches than with standard crutches for all subjects, and the transferred elastic energy made an important contribution to the total external work for spring-loaded crutches. No significant differences in the spatiotemporal parameters were observed. Optimized spring-loaded crutches can efficiently propel crutch walkers and could reduce the total energy expenditure in crutch walking. Further research using optimized spring-loaded crutches with respect to energy efficiency is recommended.

Biomechanics of octopedal locomotion: kinematic and kinetic analysis of the spiderGrammostola mollicoma

Despite the abundance of octapodal species and their evolutionary importance in originating terrestrial locomotion, the locomotion mechanics of spiders has received little attention so far. In this investigation we use inverse dynamics to study the locomotor performance of Grammostola mollicoma (18 g). Through 3-D kinematic measurements, the trajectory of the eight limbs and cephalothorax or abdomen allowed us to estimate the motion of the body centre of mass (COM) at different speeds. Classic mechanics of locomotion and multivariate analysis of several variables such as stride length and frequency, duty factor, mechanical external work and energy recovery, helped to identify two main gaits, a slow (speed <11 cm s(-1)) one and a fast one characterised by distinctive 3-D trajectories of COM. The total mechanical work (external + internal) calculated in the present study and metabolic data from the literature allowed us to estimate the locomotion efficiency of this species, which was less than 4%. Gait pattern due to alternating limb support, which generates asymmetrical COM trajectories and a small but consistent energy transfer between potential and kinetic energies of COM, is discussed both in terms of coordination indices and by referring to the octopod as formed by two quadrupeds in series. Analogies and differences of the newly obtained parameters with the allometric data and predictions are also illustrated.

“How pendulum‐like are siamangs? energy exchange during brachiation”

Hylobatidae (gibbons and siamangs) are known for their brachiation skills. The comparison of brachiation with a pendulum is made several times in the literature, and the costs and benefits of being pendulum-like are well described. However, the amount of energy exchange during brachiation of gibbons has rarely been determined. In this study, the amount of energy recovery (ER) during brachiation is assessed for three siamangs in a seminatural environment. The animals were recorded by four cameras while voluntarily brachiating on three different setups. The effects of locomotion speed, brachiation type, and setup on ER as well as on the external mechanical work during brachiation are determined. It is hypothesized that the amount of ER decreases with an increasing setup complexity while the external mechanical work increases. Additionally, we expect that support arm kinematics will be adjusted according to spatial complexity in order to maintain high recovery percentages. Our results show that ER is mainly determined by brachiation speed. Regardless of type of brachiation or setup, brachiation is done with a lower ER when brachiating faster. Within our limited range of setup variation, the expected effect of increasing complexity is not found. Although there is significant variation in support arm joint angles, no clear relation with speed, brachiation type, or setup is observed.

Muscle activity and time to task failure differ with load compliance and target force for elbow flexor muscles

The primary purpose of this study was to determine the influence of load compliance on time to failure during sustained isometric contractions performed with the elbow flexor muscles at four submaximal target forces. Subjects pulled against a rigid restraint during the force task and maintained a constant elbow angle, while supporting an equivalent inertial load during the position task. Each task was sustained for as long as possible. Twenty-one healthy adults (23 ± 6 yr; 11 men) participated in the study. The maximal voluntary contraction (MVC) force was similar (P = 0.95) before the subjects performed the force and position tasks at each of the four target forces: 20, 30, 45, and 60% of MVC force. The time to task failure was longer for the force tasks (576 ± 80 and 325 ± 70 s) than for the position tasks (299 ± 77 and 168 ± 35 s) at target forces of 20 and 30% (P < 0.001), but was similar for the force tasks (178 ± 35 and 86 ± 14 s) and the position tasks (132 ± 29 and 87 ± 14 s) at target forces of 45 and 60% (P > 0.19). The briefer times to failure for the position task at the lower forces were accompanied by greater rates of increase in elbow flexor muscle activity, mean arterial pressure, heart rate, and rating of perceived exertion. There was no difference in the estimates of external mechanical work at any target force. The dominant mechanisms limiting time to failure of sustained isometric contractions with the elbow flexor muscles appear to change at target forces between 30 and 45% MVC, with load compliance being a significant factor at lower forces only.

Mechanical Work and Metabolic Cost of Walking after Weight Loss in Obese Adolescents

This study was performed to investigate whether changes in biomechanical parameters of walking explain the reduction in net metabolic cost after weight loss in obese adolescents. Body composition and metabolic and mechanical energy costs of walking at 1.25 m·s(-1) were assessed in 16 obese adolescents before and after a weight loss. Center of mass (COM) and foot accelerations were measured using two inertial sensors and integrated twice to determine COM and foot velocities and displacements. Potential and kinetic energy fluctuations of the COM and the external mechanical work were calculated. Lateral leg swing was calculated from foot displacements. As expected, the decrease in net metabolic cost was greater, which would have been expected on the basis of the amount of weight loss. The smaller lateral leg swing after weight loss did not explain part of the decrease in net metabolic cost. The reduced body mass required less leg muscle work to raise and accelerate the COM as well as to support body weight. The decrease in body mass seems also associated with a lesser leg muscle work required to raise the COM because of smaller vertical motions. As a result of the inverted pendulum mechanism, the decrease in vertical motions (hence in potential energy fluctuations) was probably related to the decrease in mediolateral kinetic energy fluctuations. Moreover, the lesser amount of fat mass in the gynoid region seems related to the decrease in net metabolic cost of walking. The reduction in net metabolic cost of walking after weight loss in weight-reduced adolescents is associated with changes in the biomechanical parameters of walking.

External mechanical work while jumping over an obstacle at different running speeds

During running, the duration of the aerial phase depends on the vertical velocity (V v) and vertical height (S v) of the centre of mass of the body (COM) at the end of the contact phase. When the r...

Metabolic cost and mechanical work during walking after tibiotalar arthrodesis and the influence of footwear

Background This study examined metabolic energy cost and external mechanical work for step-to-step transitions after tibiotalar arthrodesis, and the effect of MBT rocker bottom shoes. Methods Oxygen uptake, forceplate and kinematic data were recorded in 18 controls and 15 patients while walking at a fixed speed of 1.25 m/s in three walking conditions: barefoot, normal walking shoes and MBT rocker bottom shoes. Metabolic energy cost, external mechanical work, and the roll-over shape of the ankle–foot complex were analyzed. Findings Tibiotalar arthrodesis leads to higher metabolic energy cost during walking. During step-to-step transitions positive work during push-off with the impaired ankle was decreased but negative work during collision was not affected. The roll-over shape of the ankle–foot complex did not differ between groups and shoe conditions. However, both in patients and controls rocker bottom shoes did lead to decreased positive work at push-off and increased negative work at collision and consequently higher metabolic energy cost of walking. Interpretation External mechanical work for step-to-step transitions is not different between patients and controls and could not account for the higher metabolic energy cost in patients. Apparently, patients adopt a different walking strategy that limits step-to-step transition cost but nevertheless induces a higher metabolic energy cost. Despite restricted ankle movement, patients retain a normal roll-over shape of the ankle–foot complex. MBT shoes do not affect roll-over shape and appear to have a counterproductive effect on step-to-step transition cost and walking economy.

Knee Musculotendon Work vs. Knee Joint Mechanical Work During Single Leg Squatting

Joint mechanical work (JMW) is commonly used to measure total muscle contributions during movement. However this measure is limited because it does not account for co-contracting muscle pairs and muscle tendon elastic properties. Previous work has found JMW underestimated the total musculotendon work (MTW) in an asymmetrical limb movement (walking) (1). Our hypothesis was that knee MTW and knee JMW would be similar during a symmetrical movement. PURPOSE: To compare both net and absolute knee JMW and knee MTW during single leg squatting. METHODS: 12 healthy volunteers (5 males and 7 females) with a history of lower extremity resistance training, were selected for participation. Each subject was outfitted for motion analysis and EMG analysis. Participants performed 16 single leg squats and the first 10 acceptable trials were used for analysis. Joint mechanical work was calculated as the time integral of net knee joint power from inverse dynamics. Musculotendon power and work were ultimately calculated from 1) quadriceps, hamstrings, and gastrocnemius muscle forces computed using a Hill-type muscle model incorporating normalized EMG and model kinematics and 2) the corresponding muscle shortening and lengthening velocities. Group mean comparisons and single-subject comparisons between JMW and MTW were made. RESULTS: Mean net JMW (-2.78±7.9J) was not significantly different from mean net MTW (-6.3±18.7J; P>.05). Mean absolute JMW (148.59±60.28J) was not significantly different from mean absolute MTW (144.16±78.82J; P>.05). Differences between JMW and MTW varied on a single-subject basis ranging from <1-48J (net) and 1-156J (absolute). CONCLUSION: In our symmetrical squatting movement, JMW calculations appear sufficient in estimating MTW. Large discrepancies however existed in a few subjects suggesting that physiological factors incorporated in musculotendon work including muscle co-contraction and musculotendon elastic properties cannot be accounted for with mechanically-based joint work in some individuals. 1.) Sasaki, K., Neptune, R., Kautz, S. The relationships between muscle, external, internal and joint mechanical work during normal walking. J Exp Bio. 212, 738-744.

Age-related changes in mechanical and metabolic energy during typical gait

The purpose of the study was to investigate and report age-related changes in walking energy expenditure using different methods of energy estimation. For 81 children and 16 adults (3–35 years) energy expenditure was investigated by using the following methods: analysis of energy changes of the centre of body mass (external and internal mechanical work), sum of segmental energies, sum of net joint work and gross and net metabolic cost, as well as net non-dimensional oxygen cost. Different methods of energy estimation not only show different outcome results but also different age-related changes. Significant changes were found for negative net joint work, external mechanical work and recovery as well as sum of segmental energies, until 9, 11 and 19 years respectively. Positive net joint work showed no differences between age groups and the differences for internal work did not suggest development. Metabolic energy showed significant changes until adult age. Gross cost decreases with increasing age in children and, although more gradually, still in adolescents. Net and net non-dimensional cost shows a more constant decrease with increasing age until adulthood. Therefore, the choice of estimation method and the use of age-related reference data when evaluating young patients should be carefully considered. For interpretation of oxygen consumption in children the use of net is superior to gross cost, but even after net non-dimensional normalization, age-related reference data should be used.

The influence of foot posture on the cost of transport in humans

Although humans appear to be specialized for endurance running, the plantigrade posture of our feet, in which the heel contacts the substrate at the beginning of a step, seems incompatible with economical running. In this study, we tested the hypothesis that plantigrade foot posture reduces the energetic cost of transport (COT) during walking in humans. When human subjects walked with their heels slightly elevated in a 'low-digitigrade' posture, COT increased by 53% above that of normal plantigrade walking. By contrast, there was no difference in COT when subjects ran with digitigrade versus plantigrade foot posture. Stride frequency increased and stride length decreased when subjects switched to digitigrade walking; however, this change did not influence the COT. Additionally, we found that possible reductions in postural stability appear not to have caused the elevated cost of digitigrade walking. Digitigrade walking, however, did (1) increase the external mechanical work performed by the limbs; (2) reduce the pendular exchange of kinetic and potential energy of the center of mass; (3) increase the average ground reaction force moment at the ankle joint; and (4) increase the recruitment of major extensor muscles of the ankle, knee, hip and back. These observations suggest that plantigrade foot posture improves the economy of walking. Relative to other mammals, humans are economical walkers, but not economical runners. Given the great distances hunter-gatherers travel, it is not surprising that humans retained a foot posture, inherited from our more arboreal great ape ancestors, that facilitates economical walking.

Metabolic energy cost and external mechanical work of walking after ankle arthrodesis using different types of footwear

Metabolic energy cost and external mechanical work of walking after ankle arthrodesis using different types of footwear

Experimental Study on Energy Dissipation of Electrolytes in Nanopores

When a nonwetting fluid is forced to infiltrate a hydrophobic nanoporous solid, the external mechanical work is partially dissipated into thermal energy and partially converted to the liquid-solid interface energy to increase its enthalpy, resulting in a system with a superior energy absorption performance. To clarify the energy dissipation and conversion mechanisms, experimental infiltration and defiltration tests of liquid/ion solutions into nanopores of a hydrophobic ZSM-5 zeolite were conducted. The characteristics of energy dissipation were quantified by measuring the temperature variation of the immersed liquid environment and compared against that estimated from pressure-infiltration volume isotherms during infiltration and defiltration stages of the test. Both stages were observed to be endothermic, with the temperature of the liquid phase showing a steady increase with changes in liquid saturation. The confinement of the molecular-sized pore space causes the liquid molecules/ions to transit between statuses of orderly and disorderly motions, resulting in dissipation behaviors that vary with liquid infiltration/defiltration rates and the types and concentrations of additive electrolytes in the liquid-both factors of which alter the characteristics of the nanofluidic transport behavior.

Effects of starting strategy on 5-min cycling time-trial performance

The importance of pacing for middle-distance performance is well recognized, yet previous research has produced equivocal results. Twenty-six trained male cyclists ([Vdot]O2peak 62.8 ± 5.9 ml · kg−1 · min−1; maximal aerobic power output 340 ± 43 W; mean ± s) performed three cycling time-trials where the total external work (102.7 ± 13.7 kJ) for each trial was identical to the best of two 5-min habituation trials. Markers of aerobic and anaerobic metabolism were assessed in 12 participants. Power output during the first quarter of the time-trials was fixed to control external mechanical work done (25.7 ± 3.4 kJ) and induce fast-, even-, and slow-starting strategies (60, 75, and 90 s, respectively). Finishing times for the fast-start time-trial (4:53 ± 0:11 min:s) were shorter than for the even-start (5:04 ± 0:11 min:s; 95% CI = 5 to 18 s, effect size = 0.65, P < 0.001) and slow-start time-trial (5:09 ± 0:11 min:s; 95% CI = 7 to 24 s, effect size = 1.00, P < 0.001). Mean [Vdot]O2 during the fast-start trials (4.31 ± 0.51 litres · min−1) was 0.18 ± 0.19 litres · min−1 (95% CI = 0.07 to 0.30 litres · min−1, effect size = 0.94, P = 0.003) higher than the even- and 0.18 ± 0.20 litres · min−1 (95% CI = 0.5 to 0.30 litres · min−1, effect size = 0.86, P = 0.007) higher than the slow-start time-trial. Oxygen deficit was greatest during the first quarter of the fast-start trial but was lower than the even- and slow-start trials during the second quarter of the trial. Blood lactate and pH were similar between the three trials. In conclusion, performance during a 5-min cycling time-trial was improved with the adoption of a fast- rather than an even- or slow-starting strategy.

Obesity does not increase external mechanical work per kilogram body mass during walking

Walking is the most common type of physical activity prescribed for the treatment of obesity. The net metabolic rate during level walking (W/kg) is ~10% greater in obese vs. normal weight adults. External mechanical work (Wext) is one of the primary determinants of the metabolic cost of walking, but the effects of obesity on Wext have not been clearly established. The purpose of this study was to compare Wext between obese and normal weight adults across a range of walking speeds. We hypothesized that Wext (J/step) would be greater in obese adults but Wext normalized to body mass would be similar in obese and normal weight adults. We collected right leg three-dimensional ground reaction forces (GRF) while twenty adults (10 obese, BMI=35.6kg/m2 and 10 normal weight, BMI=22.1kg/m2) walked on a level, dual-belt force measuring treadmill at six speeds (0.50–1.75m/s). We used the individual limb method (ILM) to calculate external work done on the center of mass. Absolute Wext (J/step) was greater in obese vs. normal weight adults at each walking speed, but relative Wext (J/step/kg) was similar between the groups. Step frequencies were not different. These results suggest that Wext is not responsible for the greater metabolic cost of walking (W/kg) in moderately obese adults.

Pound for pound: Working out how obesity influences the energetics of walking

Childhood and adult obesity are both serious health problems that are catalyzed by inadequate physical activity and the resulting chronic energy imbalance. For most people, walking consumes more metabolic energy than any other daily activity. Thus it is important to understand the energetic cost of

The energy cost for the step-to-step transition in amputee walking

The purpose of this study was to investigate whether the increased energy cost of amputee gait could be accounted for by an increase in the mechanical work dissipated during the step-to-step transition in walking. Eleven transtibial amputees (AMP) and 11 age-matched controls (CO) walked at both comfortable (CWS) and fixed (FWS, 1.3m/s) walking speed, while external mechanical work of each separate leg and metabolic energy consumption were measured. At FWS the metabolic energy consumption (Ėmet) was significantly higher in AMP compared to CO (3.34Jkg−1s−1 vs. 2.73Jkg−1s−1). At CWS, no difference in energy consumption was found (3.56Jkg−1s−1 vs. 3.58Jkg−1s−1) but CWS was significantly lower in AMP compared to CO (1.35ms−1 vs. 1.52ms−1). In conjunction with the higher Ėmet at FWS, the negative work generated by the intact leading leg for the step-to-step transition in double support was significantly higher for AMP than CO at FWS. A moderate though significant correlation was found between negative mechanical power generated during the step-to-step transition and metabolic power (CWS: r=−0.56, p=0.007; FWS: r=−0.50, p=0.019). Despite the difference in negative work during the step-to-step transition, the total absolute mechanical work over a stride did not differ between groups. This could possibly be attributed to exchange of internal positive and negative work during single support, which remains unnoticed in the external work calculations. It was concluded that the increased mechanical work for the step-to-step transition from prosthetic to intact limb contributes to the increased metabolic energy cost of amputee walking.