Energy cost of running uphill as compared to running on the level with impeding horizontal forces.

PURPOSE: We have previously shown that accelerated running on flat terrain is biomechanically equivalent to running uphill at a constant speed. This hypothesis was further investigated comparing the energy cost of running at a constant speed either uphill, or on flat terrain against an equivalent horizontal impeding force, mimicking acceleration. METHODS: Steady-state O2 consumption and the corresponding energy cost (per unit body mass and distance) were determined on 12 male subjects during treadmill running at speeds between 2.11 and 2.89 m/s: (i) on the level, (ii) uphill at 10 or 20% incline ( I ), or (iii) on the level against a horizontal traction force of 10 or 20% of the subject's body weight ( TF ). This allowed us to estimate the net efficiency ( n e t η ) of running against horizontal or vertical forces, as given by the ratio between the additional mechanical work output under TF , or the corresponding I condition, and the difference between the appropriate energy cost above that for running at constant speed on flat terrain. RESULTS: The n e t η values when running uphill ( I ) amount to 0.35-0.40, whereas those for running against an equivalent impeding force ( TF ) are about 10% greater (0.45-0.50), a fact that may be due to a greater recovery of elastic energy in the TF as compared to the I condition. CONCLUSION: Making allowance for these small differences, these data support the view of considering accelerated running on flat terrain biomechanically equivalent to running at a constant speed, up an equivalent slope.

Plyometric exercise improves jumping performance and skeletal muscle contractile properties in seniors.

OBJECTIVE: This study investigated the effects of an 8-week plyometric training (PT) session on countermovement jump (CMJ) height, take-off velocity, and Tensiomyography (TMG) derived contractile parameters in seniors. METHODS: Twenty-three senior adults (age 66.7±5.2 years) were randomly divided into two groups: PLYO (n=11) and CTRL (n=12). Tensiomyography was measured in vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), gastrocnemius medialis (GM), and lateralis (GL). Additionally, the electromechanical efficiency (EME) index was calculated in GM as a ratio between amplitudes of peak-to-peak M-wave and TMG (Dm) responses. Biochemical markers of muscle damage and inflammation were evaluated to provide indirect indices of exercise protocol safety. RESULTS: The main effect of time (for take-off velocity p=.023; ɳ2= .236) and group x time interactions (for CMJ, Tc (BF, GM), Dm (BF) and EME p<.05; ɳ2= .136 - .236) were observed. Post hoc analysis showed a significant increase in CMJ height and take-off velocity, namely by 14.2% (p=.001) and 8.2% (p=.01) in PLYO, respectively. Contraction time (Tc) decreased in BF -5.7% (p=.001) and GM -9.6% (p=.001). Dm decreased only in BF -20.8% (p=.001), while the EME index of the GM improved by 22.9% (p=.002). There were no differences between groups or assessment time points for C-reactive protein (p=.122). CONCLUSION: The present study clearly supports the application of supervised PT exercise in seniors, since explosive power, muscle contractility, and EME of the lower limbs were markedly improved after training.

Tensiomyographic Assessment of Muscle Contractile Properties in 9- to 14-Year Old Children.

While there are numerous data on the skeletal muscle fiber type composition in adults, little is known about the changes in fiber type composition and contractile properties during maturational growth in children. Using noninvasive tensiomyography, we measured contraction time (Tc), an indirect estimate of the myosin heavy chain I (MHC-I) proportion, to assess the longitudinal changes of the biceps brachii (BB), biceps femois (BF), vastus lateralis (VL), and erector spinae (ES) muscles in 53 boys and 54 girls. The children were 9 years at the start of the study and returned for 5 follow-up measurements until the age of 14 years. The ES has the shortest and the BF has the longest Tc. The VL and ES of boys have shorter Tc than those of girls. When applying the relationship between proportion of MHC-I and Tc established in adults to children's TMG data, we found a slow-to-fast transition in the VL between, at least, the ages of 6 to 10 years, when it stabilized to adult proportions. Regular participation in sports was associated with a faster BF, but not in the VL. Our data represents a first non-invasive indication of the developmental changes in muscle fiber type composition in children.

Tensiomyography detects early hallmarks of bed-rest-induced atrophy before changes in muscle architecture.

In young and older people, skeletal muscle mass is reduced after as little as 7 days of disuse. The declines in muscle mass after such short periods are of high clinical relevance, particularly in older people who show a higher atrophy rate and a slower or even a complete lack of muscle mass recovery after disuse. Ten men (24.3 yr; SD 2.6) underwent 35 days of 6° head-down tilt bed rest, followed by 30 days of recovery. During bed rest, a neutral energy balance was maintained, with three weekly passive physiotherapy sessions to minimize muscle soreness and joint stiffness. All measurements were performed in a hospital at days 1-10, 16, 28, and 35 of bed rest (BR1-BR10, BR16, BR28, and BR35, respectively) and days 1, 3, and 30 after reambulation (R + 1, R + 3, and R + 30, respectively). Vastus medialis obliquus (VMO), vastus medialis longus (VML), and biceps femoris (BF) thickness (d) and pennation angle (Θ) were assessed by ultrasonography, whereas twitch muscle belly displacement (Dm) and contraction time (Tc) were assessed with tensiomyography (TMG). After bed rest, d and Θ decreased by 13-17% in all muscles ( P < 0.001) and had recovered at R + 30. Dm was increased by 42.3-84.4% ( P < 0.001) at BR35 and preceded the decrease in d by 7, 5, and 3 days in VMO, VML, and BF, respectively. Tc increased only in BF (32.1%; P < 0.001) and was not recovered at R + 30. TMG can detect early bed-rest-induced changes in muscle with higher sensitivity before overt architectural changes, and atrophy can be detected. NEW & NOTEWORTHY Detection of early atrophic processes and irreversible adaptation to disuse are of high clinical relevance. With the use of tensiomyography (TMG), we detected early atrophic processes before overt architectural changes, and atrophy can be detected using imaging technique. Furthermore, TMG detected irreversible changes of biceps femoris contraction time.

Active workstation allows office workers to work efficiently while sitting and exercising moderately.

OBJECTIVE: To determine the effects of a moderate-intensity active workstation on time and error during simulated office work. METHODS: The aim of the study was to analyse simultaneous work and exercise for non-sedentary office workers. We monitored oxygen uptake, heart rate, sweating stains area, self-perceived effort, typing test time with typing error count and cognitive performance during 30 min of exercise with no cycling or cycling at 40 and 80 W. RESULTS: Compared baseline, we found increased physiological responses at 40 and 80 W, which corresponds to moderate physical activity (PA). Typing time significantly increased by 7.3% (p = 0.002) in C40W and also by 8.9% (p = 0.011) in C80W. Typing error count and cognitive performance were unchanged. CONCLUSIONS: Although moderate intensity exercise performed on cycling workstation during simulated office tasks increases working task execution time with, it has moderate effect size; however, it does not increase the error rate. Participants confirmed that such a working design is suitable for achieving the minimum standards for daily PA during work hours.