Locomotion as a powerful model to study integrative physiology: Efficiency, economy, and power relationship

Locomotion is the most common form of movement in nature. Its study allows analysis of interactions between muscle functions (motor) and lever system arrangements (transmission), thereby facilitating performance analysis of various body organs and systems. Thus, it is a powerful model to study various aspects of integrative physiology. The results of this model can be applied in understanding body functions and design principles as performance outputs of interest for medical and biological sciences. The overall efficiency (effoverall) during locomotion is an example of an integrative parameter, which results from the ratio between mechanical output and metabolic input. Although the concepts of cost (i.e., metabolic expenditure relative to distance) and power (i.e., metabolic expenditure relative to time) are included in its calculation, the effoverall establishes peculiar relations with these variables. For a better approach to these aspects, in this study, we presented the physical-mathematical formulation of efficiency, as well as its conceptual definitions and applications. Furthermore, the concepts of efficiency, cost, and power are discussed from the biological and medical perspectives. Terrestrial locomotion is a powerful model to study integrative physiology in humans, because by analyzing the mechanical and metabolic determinants, we may verify the efficiency and economy relationship through locomotion type, and its characteristics and restrictions. Thus, it is possible to elaborate further on various improved intervention strategies, such as physical training, competition strategies, and ergogenic supplementation

Scale model on performance prediction in recreational and elite endurance runners

Purpose: To identify the effect of allometric scaling on the relationship between running efficiency (REff) and middle-distance-running performance according to performance level. Methods: Thirteen male recreational middle-distance runners (mean ± SD age 33.3 ± 8.4 y, body mass 76.4 ± 8.6 kg, maximal oxygen uptake [VO2max] 52.8 ± 4.6 mL · kg-1 · min-1; G1) and 13 male high-level middle-distance runners (age 25.5 ± 4.2 y, body mass 62.8 ± 2.7 kg, VO2max 70.4 ± 1.9 mL · kg-1 · min-1; G2) performed a continuous incremental test to volitional exhaustion to determine VO2max and a 6-min submaximal running test at 70% of VO2max to assess REff. Results: Significant correlation between REff and performance were found for both groups; however, the strongest correlations were observed in recreational runners, especially when using the allometric exponent (respectively for G1, nonallometric vs allometric scaling: r =.80 vs r =.86; and for G2, nonallometric vs allometric scaling: r =.55 vs r =.50). Conclusion: These results indicate that an allometric normalization may improve endurance-performance prediction from REff values in recreational, but not in elite, runners. © 2014 Human Kinetics, Inc

Examination of the Relationship Among Balance, Physical Activity, and Anthropometry in Athletes With Visual Impairments

Introduction: Although it is well documented in the literature that individuals with visual impairments have low physical activity levels and impaired body compositions and postural controls compared with peers without vision loss, the relation between these parameters in athletes with visual impairments is unknown. Research Question: Here, we (i) evaluated the physical activity levels, balance measures, and anthropometry parameters in athletes with visual impairments and peers without vision loss controls and (ii) compared these variables between the two groups. Methods: We designed a retrospective observational study with parallel groups conducted on 33 athletes with visual impairments and 33 sighted controls matched for age and sex. We also utilized a questionnaire about physical activity levels and assessed static balance for 4 conditions (eyes-open firm surface, eyes-closed firm surface, eyes-open foam surface, and eyes-closed foam surface) and anthropometry. Results: In athletes with visual impairments, body composition, body mass index (BMI), physical activity level, and static balance parameters revealed no significant relationship (p >.05), whereas eyes-open and -closed firm and foam surface conditions were positively related with physical activity at a moderate level (r = 0.39, r = 0.38, p .05). Discussion: Sports participation from individuals with visual impairments is related to higher physical activity levels, resulting in better anthropometric profile. The balance control was not related to physical activity levels in athletes with visual impairments

Possible changes in energy-minimizer mechanisms of locomotion due to chronic low back pain - A literature review

One goal of the locomotion is to move the body in the space at the most economical way possible. However, little is known about the mechanical and energetic aspects of locomotion that are affected by low back pain. And in case of occurring some damage, little is known about how the mechanical and energetic characteristics of the locomotion are manifested in functional activities, especially with respect to the energy-minimizer mechanisms during locomotion. This study aimed: a) to describe the main energy-minimizer mechanisms of locomotion; b) to check if there are signs of damage on the mechanical and energetic characteristics of the locomotion due to chronic low back pain (CLBP) which may endanger the energy-minimizer mechanisms. This study is characterized as a narrative literature review. The main theory that explains the minimization of energy expenditure during the locomotion is the inverted pendulum mechanism, by which the energy-minimizer mechanism converts kinetic energy into potential energy of the center of mass and vice-versa during the step. This mechanism is strongly influenced by spatio-temporal gait (locomotion) parameters such as step length and preferred walking speed, which, in turn, may be severely altered in patients with chronic low back pain. However, much remains to be understood about the effects of chronic low back pain on the individual's ability to practice an economic locomotion, because functional impairment may compromise the mechanical and energetic characteristics of this type of gait, making it more costly. Thus, there are indications that such changes may compromise the functional energy-minimizer mechanisms

Comparison between two methods for determination of mechanical power in vertical jumping

The aim of this study was to compare the mechanical power values of vertical jumps measured by BOSCO test (Theoretical Power, PT) with mechanical power values registered by force plate (Experimenal Power, PE) and verify the agreement between the two methods. Eleven recreational runners performed continuous maximal jumps for 60 seconds. Force platform 3D and 2D kinematics system were used for calculation of PT and PE, respectively. Data about flight time and number of hops were obtained from the kinematic analysis (Dvideow 5.0). We used Bland & Altman for agreement between the methods. The average values of PT and PE were 15.6 ±2.4 W.kg-1 and 20.8 ±3.2 W.kg-1, respectively, ranging from the agreement limits ±2 s.d. Therefore, the equation of the PT is a convenient method for determining the mechanical power during continuous vertical jumps

Old men running: Mechanical work and elastic bounce

It is known that muscular force is reduced in old age. We investigate what are the effects of this phenomenon on the mechanics of running. We hypothesized that the deficit in force would result in a lower push, causing reduced amplitude of the vertical oscillation, with smaller elastic energy storage and increased step frequency. To test this hypothesis, we measured the mechanical energy of the centre of mass of the body during running in old and young subjects. The amplitude of the oscillation is indeed reduced in the old subjects, resulting in an approximately 20% smaller elastic recovery and a greater step frequency (3.7 versus 2.8Hz, p=1.9×10-5, at 15-17kmh-1). Interestingly, the greater step frequency is due to a lower aerial time, and not to a greater natural frequency of the system, which is similar in old and young subjects (3.6 versus 3.4Hz, p=0.2). Moreover, we find that in the old subjects, the step frequency is always similar to the natural frequency, even at the highest speeds. This is at variance with young subjects who adopt a step frequency lower than the natural frequency at high speeds, to contain the aerobic energy expenditure. Finally, the external work to maintain the motion of the centre of mass is reduced in the old subjects (0.9 versus 1.2Jkg-1m-1, p=5.1×10-6) due to the lower work done against gravity, but the higher step frequency involves a greater internal work to reset the limbs at each step. The net result is that the total work increases with speed more steeply in the old subjects than in young subjects. © 2007 The Royal Society

Mechanical work and long-distance performance prediction: The influence of allometric scaling

The purpose of this study was to examine the effect of allometric scaling on the relationship between mechanical work and long-distance running performance in recreational runners. Fourteen recreational long-distance runners (male, mean ± SD - age: 29 ± 7 years; body mass: 70.0 ± 10.2 kg; body height: 1.71 ± 0.07 m; maximal oxygen uptake: VO 2max 52.0 ± 4.9 ml.kg-1.min-1) performed two tests: a continuous incremental test to volitional exhaustion in order to determine VO2max, and a 6-minute running submaximal test at 3.1 m.s-1, during which segments in the sagittal plane were recorded using a digital camera and the internal (Wint), external (Wext) and total (Wtot) mechanic work, in J.kg-1.m-1, was subsequently calculated. The results indicated a significant correlation between mechanical work and performance, however, the strongest correlations were observed when allometric exponents were used (respectively for Wint, Wext and Wtot; non allometric vs. allometric scaling defined by literature (0.75) or determined mathematically (0.49): r = 0.38 vs. r = 0.44 and r = 0.50; r = 0.80 vs. r = 0.83 and r = 0.82; r = 0.70 vs. r = 0.77 and r = 0.78). These results indicate that mechanical work could be used as a predictor of recreational long-distance performance and an allometric model may improve this prediction. © Editorial Committee of Journal of Human Kinetics

Transfer of strength training to running mechanics, energetics, and efficiency

To examine the effects of increased strength on mechanical work, the metabolic cost of transport (Cost), and mechanical efficiency (ME) during running. Fourteen physically active men (22.0 ± 2.0 years, 79.3 ± 11.1 kg) were randomized to a strength-training group (SG, n = 7), who participated in a maximal strength training protocol lasting 8 weeks, and a control group (CG, n = 7), which did not perform any training intervention. Metabolic and kinematic data were collected simultaneously while running at a constant speed (2.78 m·s-1). The ME was defined as the ratio between mechanical power (Pmec) and metabolic power (Pmet). The repeated measures two-way ANOVA did not show any significant interaction between groups, despite some large effect sizes (d): internal work (Wint, p = 0.265, d = -1.37), external work (Wext, p = 0.888, d = 0.21), total work (Wtot, p = 0.931, d = -0.17), Pmec (p = 0.917, d = -0.17), step length (SL, p = 0.941, d = 0.24), step frequency (SF, p = 0.814, d = -0.18), contact time (CT, p = 0.120, d = -0.79), aerial time (AT, p = 0.266, d = 1.12), Pmet (p = 0.088, d = 0.85), and ME (p = 0.329, d = 0.54). The exception was a significant decrease in Cost (p = 0.047, d = 0.84) in SG. The paired t-test and Wilcoxon test only detected intragroup differences (pre- vs. post-training) for SG, showing a higher CT (p = 0.041), and a lower Cost (p = 0.003) and Pmet (p = 0.004). The results indicate that improved neuromuscular factors related to strength training may be responsible for the higher metabolic economy of running after 8 weeks of intervention. However, this process was unable to alter running mechanics in order to indicate a significant improvement in ME

Effect of weighted sled towing on sprinting effectiveness, power and force-velocity relationship

This study aimed to compare the components of force-velocity (F-V) and power-velocity (PV) profiles and the mechanical effectiveness of force application (or force ratio±RF) among various sled-Towing loads during the entire acceleration phase of a weighted sled sprint. Eighteen sprinters performed four 50-m sprints in various conditions: unloaded; with a load corresponding to 20% of the athlete's body mass (BM); with a load of 30% BM; and with a load of 40% BM. Data were collected with five video cameras, and the images were digitised to obtain velocity from the derivation of the centre-of-mass position. F-V and P-V components and RF were estimated from sprinting velocity-Time data for each load using a validated method that is based on an inverse dynamic approach applied to the sprinter's centreof-mass (it models the horizontal antero-posterior and vertical ground reaction force components) and requires only measurement of anthropometric and spatiotemporal variables (body mass, stature and instantaneous position or velocity during the acceleration phase). The theoretical maximal velocity decreased with load compared with the unloaded condition (for 20% BM:-6%, effect size (ES) = 0,38; for 30% BM:-15%, ES = 1.02; for 40% BM:-18%, ES = 1.10). The theoretical maximal horizontal force (F0) and maximal power were not different among conditions. However, power at the end of the acceleration phase increased with load (40% BM vs 0%: 72%; ES = 2.73) as well as the maximal mechanical effectiveness (12%; ES = 0.85). The linear decrease in RF was different between 30 or 40% BM and the unloaded condition (-23%; ES = 0.74 and 0.66). Better effectiveness may be developed with 40% BM load at the beginning of the acceleration and with the various load-induced changes in the components of the F-V and P-V relationships, allowing a more accurate determination of optimal loading conditions for maximizing power