A theory of energy cost and speed of climbing

Climbing is an interesting form of quadrupedal locomotion on vertical substrates, and also a popular recreational activity. However, a theory of locomotor energetics of climbing has not been devised yet. Here we discuss an analytical model, based on simple physical principles, that gives the energy cost as a function of the vertical speed. We found that the energy cost monotonically decreases with speed, so that to minimize the energy spent to climb one should ascend at the highest possible speed. We propose that the actual climbing speed derives from the requirement of minimizing simultaneously the work per unit time as well as the work per unit length. Our predictions are in excellent agreement with measurements carried out on elite climbers

Determinants of sit-to-stand capability in the motor impaired elderly

Among the healthy elderly, sit-to-stand (STS) movement largely depends on: (a) trunk bending momentum, (b) centre of gravity (CG) position before the body rises and (c) lower limb extensor muscle strength. Because determining whether (c) improvement would affect STS capability in the motor impaired elderly (MIE) has been recommended, we studied the relative importance of (a), (b) and (c) in determining a successful fast STS movement comparing the healthy elderly with MIE with orthopaedic disorders studied before and after a rehabilitation program. Force platform was used to measure body's posture and kinematics during a STS test and therefore to assess (a), (b) and maximum vertical velocity (VVpeak), assumed as outcome measurement. Knee extensor maximal isometric voluntary contraction normalized by body mass (nMVC) was an indicator of (c). A multiple regression model was built to predict VVpeak from the three determinants of STS movement. In both groups, the model significantly determined VVpeak, with (a) and (c) being significant predictors of VVpeak and (a) being the major predictor. Rehabilitation was effective in improving nMVC. This process resulted in a change of the relative importance of (a) and (c), strength becoming the major predictor of VVpeak. In conclusion the present study demonstrates that a rehabilitative intervention aimed at increasing strength is effective in improving STS capability in MIE. © 2003 Elsevier Ltd. All rights reserved

Differences in the force/endurance relationship between young and older men

The aim of the present study was to ascertain if in six young (23-35 years) and in six older (70-72 years) healthy men matched for comparable absolute and specific maximal force of the dominant elbow flexors, differences in isometric endurance, myoelectrical fatigability, and shortening velocity are still recognizable. To assess the specific force, the muscle cross sectional area (CSA) was determined from magnetic resonance imaging (MRI) scans. The performance of the elbow flexors was studied by assessing the isometric endurance times (ET) at different percentages of maximal isometric contraction (MVC), the average muscle fibre conduction velocity of action potentials (CV), and the median frequency (MDF) of the surface electromyogram (sEMG) of the biceps brachii. Finally, the torque-velocity curve was assessed by means of maximal isokinetic contractions at six fixed angular velocities. All data were expressed as the mean (SD). The results showed that: (1) the ET was longer in the older subjects at the highest levels of isometric contraction, independently from the absolute force; (2) the modifications of muscle fibre CV during isometric effort progressed less rapidly in the older than the younger groups, as did those of MDF; and (3) at the same angular velocity, the older subjects exerted less absolute force than the younger subjects. These results suggest an impairment of the neuromuscular system of older men, which is less powerful and less fatigable than that of young men

Cardiorespiratory fitness, energy intake and cardiovascular risk in a sample of Paralympic athletes with locomotor impairment

Purpose: To evaluate the possible relationship between oxygen uptake peak (VO2peak), energy and macronutrient intakes (E&MI) and cardiovascular and inflammatory risks (CVR and InR) in a population of Paralympic athletes (PA) with a locomotor impairment (PA-LI). Methods: A retrospective chart review of the health and fitness evaluations preceding London 2012 Paralympic Games1 was performed in 46 male PA-LI. They were divided in 2 groups depending on their health conditions: 29 PA with spinal cord injury (PA-SCI, mean age: 37±8.9 years old), and 17 PA with other health conditions, e.g., lower limb amputation and poliomyelitis (PA-OHC, mean age: 35±9.1 years old). They underwent anthropometry assessment (standard and skinfold measurements); laboratory blood tests, including C reactive protein (CRP) and uric acid to estimate InR; nutritional 24-hour recall to assess energy and macronutrient intakes (E&MI); arm cranking ergometer incremental maximal exercise tests to measure VO2peak. CVR was estimated through 3 indices: fatty liver index2 (FLI), lipid accumulation product3 (LAP) and visceral adiposity index4 (VAI). FLI was calculated from body mass index (BMI), waist circumference (WC), gamma-GT and triglycerides (TG); LAP from WC and TG; VAI from BMI, WC, TG and high-density lipoprotein cholesterol. Mann-Whitney test and Spearman correlations were performed to compare the groups and to evaluate the relationship between variables, respectively. Results: In spite of no differences in E&MI, body composition and CVR indices, PA-SCI vs PA-OHC showed lower VO2peak (30±10.6 vs 37±7.9 ml/kg/min, p<0.01) and higher CRP (1.37, IQR: 0.53-1.79 vs 0.33, IQR: 0.26-0.96 mg/l, p <0.01). VO2peak/kg correlated negatively with uric acid levels (r: -0.563, p<0.0001), CRP levels (r: -0.425, p<0.01), FLI (r: -0.564, p<0.0001), LAP (r: -0.513, p=0.0001) and VAI (r: -0.558, p<0.001). Conclusion: In PA-LI VO2peak is inversely related to markers and indices of InR and CVR, suggesting a protective role of the cardiorespiratory fitness on health. Physical exercise5 and sport6 are highly recommended to improve VO2peak