Cross-country (XC) skiing is one of the most demanding of endurance sports, involving protracted competitions on varying terrain employing a variety of skiing techniques that require upper- and/or lower-body work to different extents. Through more effective training and extensive improvements in equipment and track preparation, the speed of cross-country ski races has increased more than that of any other winter Olympic sport, and, in addition, new types of racing events have been introduced. To a certain extent this has altered the optimal physiological capacity required to win, and the training routines of successful skiers have evolved accordingly. The long-standing tradition of researchers working closely with XC-ski coaches and athletes to monitor progress, improve training, and refine skiing techniques has provided unique physiological insights revealing how these athletes are approaching the upper limits of human endurance. This review summarizes current scientific knowledge concerning the demands involved in elite XC skiing, as well as the physiological capacity and training routines of the best athletes.
Øyvind Sandbakk and Hans-Christer Holmberg
Valter C. Barbosa Filho, Kelly Samara da Silva, Jorge Mota, Carmem Beck and Adair da Silva Lopes
Promoting physical activity (PA) in low- and middle-income countries is an important public health topic as well as a challenge for practice. This study aimed to assess the effect of a school-based intervention on different PA-related variables among students.
This cluster-randomized-controlled trial included 548 students in the intervention group and 537 in the control group (11–18 years-old) from 6 schools in neighborhoods with low Human Development Index (0.170–0.491) in Fortaleza, Brazil. The intervention included strategies focused on training teachers, opportunities for PA in the school environment and health education. Variables measured at baseline and again at the 4-months follow-up included the weekly time in different types of moderate-to-vigorous PA (MVPA), preference for PA during leisure-time, PA behavioral change stage and active commuting to school. Generalized linear models and binary logistic regressions were used.
An intervention effect was found by increasing the weekly time in MVPA (effect size = 0.17), popular games (effect size = 0.35), and the amount of PA per week (effect size = 0.27) among students (all P < .05).
The intervention was effective in promoting improvements in some PA outcomes, but the changes were not sufficient to increase the proportion of those meeting PA recommendations.
Tetsuro Muraoka, Tadashi Muramatsu, Hiroaki Kanehisa and Tetsuo Fukunaga
The aim of the present study was to determine the transverse strain of aponeuroses in human tibialis anterior muscle (TA) in vivo and to clarify the influence of muscle fiber length and state of contraction on the transverse strain. Sagittal and horizontal images of TA were taken in seven men and one woman at ankle angles of –20° (dorsiflexed direction), 0° (neutral anatomic position), and 45° (plantar-flexed direction) both at rest and during submaximal dorsiflexion contraction (20 Nm: 0° and 45°; 10 Nm: –20°) using B-mode ultrasonography. The width of the TA central aponeurosis changed from 21.7 ± 1.0 (mean ± SE) to 25.5 ± 1.1 mm when muscle fiber length changed from 91.0 ± 3.5 (45° in the resting state) to 55.1 ± 3.2 mm (–20° in the active state). The transverse strain of the TA central aponeurosis, which was change in relative width compared with the width at 45° in the resting state, increased when the muscle fiber length decreased. The transverse strain of the TA central aponeurosis was directly proportional to the muscle fiber length to the –1/2 power in both resting and active states (R = 0.81 and 0.74, p < 0.05 for both), and there was no significant difference (p < 0.05) between correlation coefficients and regression slopes for resting and active states. The findings suggest that the transverse strain of the TA central aponeurosis was closely related to muscle fiber length and that the transverse strain of the aponeurosis should be considered for accurate 3-D muscle modeling.
Darren G. Burke, Philip D. Chilibeck, Gianni Parise, Mark A. Tarnopolsky and Darren G. Candow
α-lipoic acid has been found to enhance glucose uptake into skeletal muscle in animal models. Studies have also found that the co-ingestion of carbohydrate along with creatine increases muscle creatine uptake by a process related to insulin-stimulated glucose disposal. The purpose of this study was to determine the effect of α-lipoic acid on human skeletal muscle creatine uptake by directly measuring intramuscular concentrations of creatine, phosphocreatine, and ad-enosine triphosphate when creatine monohydrate was co-ingested with α-lipoic acid. Muscle biopsies were acquired from the vastus lateralis m. of 16 male subjects (18–32 y) before and after the experimental intervention. After the initial biopsy, subjects ingested 20 g · d−1 of creatine monohydrate, 20 g · d−1 of creatine monohydrate + 100 g · d−1 of sucrose, or 20 g · d−1 of creatine monohydrate + 100 g · d−1 of sucrose + 1000 mg · d−1 of α-lipoic acid for 5 days. Subjects refrained from exercise and consumed the same balanced diet for 7 days. Body weight increased by 2.1% following the nutritional intervention, with no differences between the groups. There was a significant increase in total creatine concentration following creatine supplementation, with the group ingesting α-lipoic acid showing a significantly greater increase (p < .05) in phosphocreatine (87.6 → 106.2 mmol · kg−1 dry mass [dm]) and total creatine (137.8 → 156.8 mmol · kg−1 dm). These findings indicate that co-ingestion of α-lipoic acid with creatine and a small amount of sucrose can enhance muscle total creatine content as compared to the ingestion of creatine and sucrose or creatine alone.
This exploratory research investigation focused on the concept of human extensibility and sought to introduce the topic to the sport management literature. The purpose of this inquiry on human extensibility centered on attempting to better understand how professionalized sport facilities embrace communication technology to help virtual and remote spectators become extensible agents. The space-time path of both a high and low-identified sport fan was tracked through the creation of a Geographic Information System (GIS) based model to help explain the extensibility phenomenon. The GIS-based diagrams were established with the help of data collected from a space-time diary, video camera, and participant interviews. Professionalized sport facilities enjoy the space and ability to incorporate highly technical structures within their confines to help improve human extensibility, however, people must possess the resources (i.e., time and money), desire, and knowledge to exploit the technology. The researcher suggests future producers of sport products will benefit both publicly and financially with this emphasis. Finally, this research endeavor offers further discussion and predictions on newer technology emerging that professionalized sport facilities will or should likely embrace in the future to improve extensibility for all types of fans and to create, maintain, and/or secure greater fan identification.
Jos J. de Koning, Cees-Jan van der Zweep, Jesper Cornelissen and Bouke Kuiper
Optimal pacing strategy was determined for breaking the world speed record on a human-powered vehicle (HPV) using an energy-flow model in which the rider’s physical capacities, the vehicle’s properties, and the environmental conditions were included. Power data from world-record attempts were compared with data from the model, and race protocols were adjusted to the results from the model. HPV performance can be improved by using an energy-flow model for optimizing race strategy. A biphased in-run followed by a sprint gave best results.
Ronald J. Maughan, Phillip Watson, Philip A.A. Cordery, Neil P. Walsh, Samuel J. Oliver, Alberto Dolci, Nidia Rodriguez-Sanchez and Stuart D.R. Galloway
accordance with the Human Tissues Act. Stored samples were discarded once analysis was completed. All urine collected during the study was passed into a 1-L plastic container. The volume of each urine pass was determined by measuring the mass on an electronic balance, assuming a specific gravity of 1
Column-editor : Robert D. Kersey
Nicholas Stergiou, Jenny A. Kent and Denise McGrath
An optimal level of variability enables us to interact adaptively and safely to a continuously changing environment, where often our movements must be adjusted in a matter of milliseconds. A large body of research exists that demonstrates natural variability in healthy gait (along with variability in other, healthy biological signals such as heart rate) and a loss of this variability in aging and injury, as well as in a variety of neurodegenerative and physiological disorders. We submit that this field of research is now in pressing need of an innovative “next step” that goes beyond the many descriptive studies that characterize levels of variability in various patient populations. We need to devise novel therapies that will harness the existing knowledge on biological variability and create new possibilities for those in the grip of disease. We also propose that the nature of the specific physiological limitation present in the neuromuscular apparatus may be less important in the physiological complexity framework than the control mechanisms adopted by the older individual in the coordination of the available degrees of freedom. The theoretical underpinnings of this framework suggest that interventions designed to restore healthy system dynamics may optimize functional improvements in older adults. We submit that interventions based on the restoration of optimal variability and movement complexity could potentially be applied across a range of diseases or dysfunctions as it addresses the adaptability and coordination of available degrees of freedom, regardless of the internal constraints of the individual.
Slobodan Jaric, Charli Tortoza, Ismael F.C. Fatarelli and Gil L. Almeida
A number of studies have analyzed various indices of the final position variability in order to provide insight into different levels of neuromotor processing during reaching movements. Yet the possible effects of movement kinematics on variability have often been neglected. The present study was designed to test the effects of movement direction and curvature on the pattern of movement variable errors. Subjects performed series of reaching movements over the same distance and into the same target. However, due either to changes in starting position or to applied obstacles, the movements were performed in different directions or along the trajectories of different curvatures. The pattern of movement variable errors was assessed by means of the principal component analysis applied on the 2-D scatter of movement final positions. The orientation of these ellipses demonstrated changes associated with changes in both movement direction and curvature. However, neither movement direction nor movement curvature affected movement variable errors assessed by area of the ellipses. Therefore it was concluded that the end-point variability depends partly, but not exclusively, on movement kinematics.