Description:
Traumatic brain injury (TBI) is the leading cause of death in alpine skiing. It has been found that helmet use can reduce the incidence of head injuries between 15% and 60%. However, knowledge on optimal helmet performance criteria in World Cup alpine skiing is currently limited owing to the lack of biomechanical data from real crash situations. Purpose: This study aimed to estimate impact velocities in a severe TBI case in World Cup alpine skiing. Methods: Video sequences from a TBI case in World Cup alpine skiing were analyzed using a model-based image matching technique. Video sequences from four camera views were obtained in full high-definition (1080p) format. A three-dimensional model of the course was built based on accurate measurements of piste landmarks and matched to the background video footage using the animation software Poser 4. A trunk-neck-head model was used for tracking the skier's trajectory. Results: Immediately before head impact, the downward velocity component was estimated to be 8 m.s(-1). After impact, the upward velocity was 3 m.s(-1), whereas the velocity parallel to the slope surface was reduced from 33 m.s(-1) to 22 m.s(-1). The frontal plane angular velocity of the head changed from 80 radIsj1 left tilt immediately before impact to 20 rad.s(-1) right tilt immediately after impact. Conclusions: A unique combination of high-definition video footage and accurate measurements of landmarks in the slope made possible a high-quality analysis of head impact velocity in a severe TBI case. The estimates can provide crucial information on how to prevent TBI through helmet performance criteria and design.
Description:
Traumatic brain injury (TBI) is the leading cause of death in alpine skiing. It has been found that helmet use can reduce the incidence of head injuries between 15% and 60%. However, knowledge on optimal helmet performance criteria in World Cup alpine skiing is currently limited owing to the lack of biomechanical data from real crash situations. Purpose: This study aimed to estimate impact velocities in a severe TBI case in World Cup alpine skiing. Methods: Video sequences from a TBI case in World Cup alpine skiing were analyzed using a model-based image matching technique. Video sequences from four camera views were obtained in full high-definition (1080p) format. A three-dimensional model of the course was built based on accurate measurements of piste landmarks and matched to the background video footage using the animation software Poser 4. A trunk-neck-head model was used for tracking the skier's trajectory. Results: Immediately before head impact, the downward velocity component was estimated to be 8 m.s(-1). After impact, the upward velocity was 3 m.s(-1), whereas the velocity parallel to the slope surface was reduced from 33 m.s(-1) to 22 m.s(-1). The frontal plane angular velocity of the head changed from 80 radIsj1 left tilt immediately before impact to 20 rad.s(-1) right tilt immediately after impact. Conclusions: A unique combination of high-definition video footage and accurate measurements of landmarks in the slope made possible a high-quality analysis of head impact velocity in a severe TBI case. The estimates can provide crucial information on how to prevent TBI through helmet performance criteria and design.
Description:
PURPOSE: The mechanism whereby anabolic androgens are associated with hypertrophy of skeletal muscle is incompletely understood but may involve an interaction with locally generated insulin-like growth factor (IGF) 1. The present investigation utilized a cell culture model of human skeletal muscle-derived cell maturation to test the hypothesis that androgens increase differentiation of human muscle precursor cells in vitro and to assess effects of androgen with or without IGF-1 on IGF-1 messenger RNA (mRNA) expression in human muscle precursor cells. METHODS: Differentiation of muscle-derived cells was induced under standard low-serum conditions. Cultures were then exposed to androgen (testosterone (T)) at 50, 100, and 500 nM or IGF-1 (10-50 ng.mL(-)(1)). Immunocytochemistry and real-time polymerase chain reaction (RT-PCR) were used to assess effects of androgens and IGF-1 after 3- (early) or 7-d (late) muscle differentiation, respectively; RT-PCR was used to quantify the effects on androgen receptor expression. RESULTS: Under low-serum conditions, 3-d exposure to androgens or IGF-1 or both resulted in no significant increase in cellular myogenic commitment. After 7-d exposure, however, T and IGF-1 were both found to increase fusion index with no observable synergistic effect. T also increased IGF-1 mRNA generation (P < 0.0001), whereas exogenous IGF-1 (P < 0.001) reduced IGF-1 mRNA transcription relative to control. The T effect was reversible after treatment with flutamide, an androgen receptor antagonist. CONCLUSIONS: Both T and IGF-1 increase myogenic commitment after 7-d exposure to a differentiation medium. With T causing a concomitant increase in IGF-1 mRNA underpinning IGF-1 as a central mediator in the cellular pathways associated with muscle hypertrophy, including those affected by androgens. The novel system described has the potential for elucidating the pattern of growth factor effects associated with androgens in skeletal muscle.
Description:
Effectiveness of the 2006 Commonwealth Games 10,000 Steps Walking Challenge. Med. Sci. Sports Exerc., Vol. 41, No. S. pp. 1673-1680, 2009. Introduction: There is little evidence Supporting sustainability of public health interventions based upon the 10,000 steps concept conducted in "real-world" settings. This study investigated the effectiveness of the 10,000 Steps Walking Challenge, initiated in con junction with the 2006 Commonwealth Games in Melbourne. Australia, in March 2006. Methods: This study analyzed characteristics of registrants (n = 1836), pedometer counts logged onto a Web site between February 2006 and February 2007 (n = 18,032 entries by 914 participants), and two surveys of participants in June 2006 (n = 128) and December 2006 (n = 62). Results: The program reached its target population of females aged 30-49 yr (40.2% of participants), a group known to have low activity levels, which also has potential to influence the behavior of family, friends, and workmates. Compliance was poor: only 49.8% of registrants ever logged steps, and of these, only 45.5% Continued beyond the period of the challenge and 16.6% for more than 1 month. Mean (9527 +/- 297, 95% confidence interval) and median (9638) recorded steps per day came close to the target of 10,000 steps; 80.1% of participants reached 10,000 steps at least once and 21.9% did so every time they logged steps. For survey respondents who provided complete data (n = 53) the mean estimated daily steps increased significantly (P < 0.001) from 6401 +/- 884 steps before the program to 9921 +/- 1039 steps at the first survey and then fell back significantly (P = 0.026) to 8727 +/- 1284 steps at the second survey but remained significantly higher than the baseline figure (P < 0.001). Conclusion: The program had immediate effectiveness and was Sustainable for a small proportion of participants, but effectiveness was limited by problems with long-term motivation and compliance/adherence.
Description:
Effectiveness of the 2006 Commonwealth Games 10,000 Steps Walking Challenge. Med. Sci. Sports Exerc., Vol. 41, No. S. pp. 1673-1680, 2009. Introduction: There is little evidence Supporting sustainability of public health interventions based upon the 10,000 steps concept conducted in "real-world" settings. This study investigated the effectiveness of the 10,000 Steps Walking Challenge, initiated in con junction with the 2006 Commonwealth Games in Melbourne. Australia, in March 2006. Methods: This study analyzed characteristics of registrants (n = 1836), pedometer counts logged onto a Web site between February 2006 and February 2007 (n = 18,032 entries by 914 participants), and two surveys of participants in June 2006 (n = 128) and December 2006 (n = 62). Results: The program reached its target population of females aged 30-49 yr (40.2% of participants), a group known to have low activity levels, which also has potential to influence the behavior of family, friends, and workmates. Compliance was poor: only 49.8% of registrants ever logged steps, and of these, only 45.5% Continued beyond the period of the challenge and 16.6% for more than 1 month. Mean (9527 +/- 297, 95% confidence interval) and median (9638) recorded steps per day came close to the target of 10,000 steps; 80.1% of participants reached 10,000 steps at least once and 21.9% did so every time they logged steps. For survey respondents who provided complete data (n = 53) the mean estimated daily steps increased significantly (P < 0.001) from 6401 +/- 884 steps before the program to 9921 +/- 1039 steps at the first survey and then fell back significantly (P = 0.026) to 8727 +/- 1284 steps at the second survey but remained significantly higher than the baseline figure (P < 0.001). Conclusion: The program had immediate effectiveness and was Sustainable for a small proportion of participants, but effectiveness was limited by problems with long-term motivation and compliance/adherence.
Description:
Purpose: The purpose of the present study was to profile the aerobic and anaerobic energy system contribution during high-speed treadmill exercise that simulated 200-, 400-, 800-, and 1500-m track running events. Methods: Twenty highly trained athletes (Australian National Standard) participated in the study, specializing in either the 200-m (N = 3), 400-m (N = 6), 800-m (N = 5), or 1500-m (N = 6) event (mean VO2 peak [mL·kg-l-min-1] ± SD = 56 ± 2, 59 ± 1, 67 ± 1, and 72 ± 2, respectively). The relative aerobic and anaerobic energy system contribution was calculated using the accumulated oxygen deficit (AOD) method. Results: The relative contribution of the aerobic energy system to the 200-, 400-, 800-, and 1500-m events was 29 ± 4, 43 ± 1, 66 ± 2, and 84 ± 1% ± SD, respectively. The size of the AOD increased with event duration during the 200-, 400-, and 800-m events (30.4 ± 2.3, 41.3 ± 1.0, and 48.1 ± 4.5 mL·kg-1, respectively), but no further increase was seen in the 1500-m event (47.1 ± 3.8 mL·kg-1). The crossover to predominantly aerobic energy system supply occurred between 15 and 30 s for the 400-, 800-, and 1500-m events. Conclusions: These results suggest that the relative contribution of the aerobic energy system during track running events is considerable and greater than traditionally thought.
Description:
Introduction/Purpose: The objectives of this study were to examine whether a static stretching (SS) routine decreased isometric force, muscle activation, and jump power while improving range of motion (ROM). Second, the study attempted to compare the duration of the dependent variable changes with the duration of the change in ROM. Methods: Twelve participants were tested pre- and post- (POST, 30, 60, 90, and 120 min) SS of the quadriceps and plantar flexors (PF) or a similar period of no stretch (control). Measurements during isometric contractions included maximal voluntary force (MVC), evoked contractile properties (peak twitch and tetanus), surface integrated electromyographic (iEMG) activity of the agonist and antagonistic muscle groups, and muscle inactivation as measured by the interpolated twitch technique (ITT). Vertical jump (VJ) measurements included unilateral concentric-only (no countermovement) jump height as well as drop jump height and contact time. ROM associated with seated hip flexion, prone hip extension, and plantar flexion-dorsiflexion was also recorded. Results: After SS, there were significant overall 9.5% and 5.4% decrements in the torque or force of the quadriceps for MVC and ITT, respectively. Force remained significantly decreased for 120 min (10.4%), paralleling significant percentage increases (6%) in sit and reach ROM (120 min). After SS, there were no significant changes in jump performance or PF measures. Conclusion: The parallel duration of changes in ROM and quadriceps isometric force might suggest an association between stretch-induced changes in muscle compliance and isometric force output.
Description:
Does Sports Club Participation Contribute to Health-Related Quality of Life? Med. Sci. Sports Exerc., Vol. 42, No. 5, pp. 1022-1028, 2010. Given the social nature of participation in sport, we hypothesized that club sports participants would have greater well-being and quality of life than participants in other forms of physical activity (PA). Purpose: The purpose of this study was to examine health-related quality of life and life satisfaction in women who participate in three contrasting forms of PA: club sport, gym activities, and walking. Methods: This was a cross-sectional study of the relationship between type of PA setting and measures of health-related quality of life (Short-Form Health Survey [SF-36]) and life satisfaction in 818 women living in rural Victoria, Australia, in 2007. Data were also compared with those from a normative sample of 2345 women. Results: After adjustment for potential confounders (age,! education, marital status, children aged <16 yr, perceived financial stress, and level of recreational PA), four of the eight SF-36 subscales, the SF-36 mental health component summary score, and life satisfaction were significantly higher in the club sport group than that in the other groups. Conclusion: Although cross-sectional research cannot establish causal links, the results suggest that participation in club sport may enhance the health benefits of PA.
Description:
Does Sports Club Participation Contribute to Health-Related Quality of Life? Med. Sci. Sports Exerc., Vol. 42, No. 5, pp. 1022-1028, 2010. Given the social nature of participation in sport, we hypothesized that club sports participants would have greater well-being and quality of life than participants in other forms of physical activity (PA). Purpose: The purpose of this study was to examine health-related quality of life and life satisfaction in women who participate in three contrasting forms of PA: club sport, gym activities, and walking. Methods: This was a cross-sectional study of the relationship between type of PA setting and measures of health-related quality of life (Short-Form Health Survey [SF-36]) and life satisfaction in 818 women living in rural Victoria, Australia, in 2007. Data were also compared with those from a normative sample of 2345 women. Results: After adjustment for potential confounders (age,! education, marital status, children aged <16 yr, perceived financial stress, and level of recreational PA), four of the eight SF-36 subscales, the SF-36 mental health component summary score, and life satisfaction were significantly higher in the club sport group than that in the other groups. Conclusion: Although cross-sectional research cannot establish causal links, the results suggest that participation in club sport may enhance the health benefits of PA.