Peak anaerobic power in elderly men

The relationship of maximal anaerobic power (P _max) of the quadriceps muscle and corresponding optimal shortening velocity (v _opt) with age, habitual physical activity (PA) and maximal oxygen consumption (V˙O_{2 max} ) were assessed in 37 healthy older [71.1?(SD 3.8) years] men and compared to those of 16 young [22.7 (SD 3.4) years] men. The PA was evaluated using a?questionnaire. The P _max and v _opt were measured on a friction loaded non-isokinetic cycle ergometer. The P _max was expressed relative to body mass –P _{max · kg?1}, and relative to the mass of the two quadriceps muscles –P _{max · kgquad?1}. The decline of P _{max · kg?1} from youth to advanced age (8.3% per decade) was greater than the decrease in quadriceps muscle mass (3.8% per decade), in P _{max · kgquad?1} (5.9% per decade) and in v _opt (4.3% per decade). In the older men, a negative relationship of P _{max · kg?1} (r?=??0.33) and P _{max · kgquad?1} (r?=??0.44) with age was found. Ergometer measurements were not correlated with PA activity indices or V˙O_{2 max} , while V˙O_{2 max} was positively associated with PA. In a multiple stepwise regression analysis age was the only variable that contributed significantly to P _{max · kg?1}?and P _{max · kgquad?1}?variances. Our findings indicated that in these healthy elderly men, unlike the fall in V˙O_{2 max} , habitual PA did not attenuate the decline in P _max of the quadriceps muscle with age. This finding was different from a previously described relationship in older women and would suggest sex differences in determining P _max in healthy older subjects.     

Physiological demands of different sailing techniques of the new Olympic windsurfing class

The introduction of the new Olympic class windsurf-board has prompted sailors to develop a new technique of sail “pumping” (rhythmically pulling the sail so that it acts as a wing). Contrary to the old technique that mainly involved upper body activity, the new one requires both upper and lower body muscle activity. Accordingly, the aim of the present study was to compare the performance characteristics of the board (speed and pointing angle ability relative to the direction of the wind) as well as the sailors’ physiological demands during sail pumping with the old and new pumping techniques. Nineteen male, highly-trained (O_2max: 65.1 ± 5.9 ml min⁻¹ kg⁻¹), international level windsurfers from six different countries underwent two testing sessions on-water in a balanced order. Compared to the old pumping technique the mean distance sailed with the new technique (1,872 ± 15 and 1,764 ± 13 m, respectively) and the board speed (3.42 ± 0.49 and 3.81 ± 0.28 m s⁻¹, respectively) were significantly (P < 0.05) shorter and greater, respectively. Consequently, the time taken to sail the testing course was significantly shorter with the new compared to the old technique (390 ± 8 vs. 420 ± 16 s). Despite the finding that the new technique was sustained at a significantly higher fraction of O_2max (80.5 ± 5.2 and 72.7 ± 4.5%, respectively) compared to the old technique, total energy expenditure (130.7 ± 11.3 and 128.1 ± 9.2 Kcal, respectively) and blood lactate concentration 3 min into recovery (9.4 ± 2.2 and 8.5 ± 1.7 mmol l⁻¹, respectively) were not different. It is concluded that application of the new sail pumping technique improves the performance characteristics of the board without increasing the sailors’ total metabolic requirement.     

Sequential activation of axial muscles during different forms of rhythmic behavior in man

In humans, studies of back muscle activity have mainly addressed the functioning of lumbar muscles during postural adjustments or rhythmic activity, including locomotor tasks. The present study investigated how back muscles are activated along the spine during rhythmical activities in order to gain insights into spinal neuronal organization. Electromyographic recordings of back muscles were performed at various trunk levels, and changes occurring in burst amplitudes and phase relationships were analyzed. Subjects performed several rhythmic behaviors: forward walking (FW), backward walking (BW), amble walking (where the subjects moved their arms in phase with the ipsilateral leg), walking on hands and knees (HK) and walking on hands with the knees on the edge of a treadmill (Hand). In a final task, the subjects were standing and were asked to swing (Swing) only their arms as if they were walking. It was found that axial trunk muscles are sequentially activated by a motor command running along the spinal cord (which we term “motor waves”) during various types of locomotion or other rhythmic motor tasks. The bursting pattern recorded under these conditions can be classified into three categories: (1) double-burst rhythmic activity in a descending (i.e., with a rostro-caudal propagation) motor wave during FW, BW and HK conditions; (2) double-burst rhythmic activity with a stationary motor wave (i.e., occurring in a single phase along the trunk) during the ‘amble’ walk condition; (3) monophasic rhythmic activity with an ascending (i.e., with a caudo-rostral propagation) motor wave during the Swing and Hands conditions. Our results suggest that the networks responsible for the axial propagation of motor activity during locomotion may correspond to those observed in invertebrates or lower vertebrates, and thus may have been partly phylogenetically conserved. Such an organization could support the dynamic control of posture by ensuring fluent movement during locomotion.     

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N·kg^–1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137–180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17–214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (v _opt) and individual maximal power output (P _max) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since v _opt has been demonstrated to be related to human fibre type composition both v _opt, P _max and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.     

Designing a Pediatric Study for an Antimalarial Drug by Using Information from Adults

The objectives of this study were to design a pharmacokinetic (PK) study by using information about adults and evaluate the robustness of the recommended design through a case study of mefloquine. PK data about adults and children were available from two different randomized studies of the treatment of malaria with the same artesunate-mefloquine combination regimen. A recommended design for pediatric studies of mefloquine was optimized on the basis of an extrapolated model built from adult data through the following approach. (i) An adult PK model was built, and parameters were estimated by using the stochastic approximation expectation-maximization algorithm. (ii) Pediatric PK parameters were then obtained by adding allometry and maturation to the adult model. (iii) A D-optimal design for children was obtained with PFIM by assuming the extrapolated design. Finally, the robustness of the recommended design was evaluated in terms of the relative bias and relative standard errors (RSE) of the parameters in a simulation study with four different models and was compared to the empirical design used for the pediatric study. Combining PK modeling, extrapolation, and design optimization led to a design for children with five sampling times. PK parameters were well estimated by this design with few RSE. Although the extrapolated model did not predict the observed mefloquine concentrations in children very accurately, it allowed precise and unbiased estimates across various model assumptions, contrary to the empirical design. Using information from adult studies combined with allometry and maturation can help provide robust designs for pediatric studies.