Emma L. Sweeney, Daniel J. Peart, Irene Kyza, Thomas Harkes, Jason G. Ellis and Ian H. Walshe
Experimental sleep restriction (SR) has demonstrated reduced insulin sensitivity in healthy individuals. Exercise is well-known to be beneficial for metabolic health. A single bout of exercise has the capacity to increase insulin sensitivity for up to 2 days. Therefore, the current study aimed to determine if sprint interval exercise could attenuate the impairment in insulin sensitivity after one night of SR in healthy males. Nineteen males were recruited for this randomized crossover study which consisted of four conditions—control, SR, control plus exercise, and sleep restriction plus exercise. Time in bed was 8 hr (2300–0700) in the control conditions and 4 hr (0300–0700) in the SR conditions. Conditions were separated by a 1-week entraining period. Participants slept at home, and compliance was assessed using wrist actigraphy. Following the night of experimental sleep, participants either conducted sprint interval exercise or rested for the equivalent duration. An oral glucose tolerance test was then conducted. Blood samples were obtained at regular intervals for measurement of glucose and insulin. Insulin concentrations were higher in SR than control (p = .022). Late-phase insulin area under the curve was significantly lower in sleep restriction plus exercise than SR (862 ± 589 and 1,267 ± 558; p = .004). Glucose area under the curve was not different between conditions (p = .207). These findings suggest that exercise improves the late postprandial response following a single night of SR.
Christopher C. Webster, Kathryn M. van Boom, Nur Armino, Kate Larmuth, Timothy D. Noakes, James A. Smith and Tertius A. Kohn
Very little is known about how long-term (>6 months) adaptation to a low-carbohydrate, high-fat (LCHF) diet affects insulin signaling in healthy, well-trained individuals. This study compared glucose tolerance; skeletal muscle glucose transporter 4 (GLUT4) and insulin receptor substrate 1 (IRS1) content; and muscle enzyme activities representative of the main energy pathways (3-hydroxyacetyl-CoA dehydrogenase, creatine kinase, citrate synthase, lactate dehydrogenase, phosphofructokinase, phosphorylase) in trained cyclists who followed either a long-term LCHF or a mixed-macronutrient (Mixed) diet. On separate days, a 2-hr oral glucose tolerance test was conducted, and muscle samples were obtained from the vastus lateralis of fasted participants. The LCHF group had reduced glucose tolerance compared with the Mixed group, as plasma glucose concentrations were significantly higher throughout the oral glucose tolerance test and serum insulin concentrations peaked later (LCHF, 60 min; Mixed, 30 min). Whole-body insulin sensitivity was not statistically significantly different between groups (Matsuda index: LCHF, 8.7 ± 3.4 vs. Mixed, 12.9 ± 4.6; p = .08). GLUT4 (LCHF: 1.13 ± 0.24; Mixed: 1.44 ± 0.16; p = .026) and IRS1 (LCHF: 0.25 ± 0.13; Mixed: 0.46 ± 0.09; p = .016) protein content was lower in LCHF muscle, but enzyme activities were not different. We conclude that well-trained cyclists habituated to an LCHF diet had reduced glucose tolerance compared with matched controls on a mixed diet. Lower skeletal muscle GLUT4 and IRS1 contents may partially explain this finding. This could possibly reflect an adaptation to reduced habitual glucose availability rather than the development of a pathological insulin resistance.
Sergei Iljukov, Jukka-Pekka Kauppi, Arja L.T. Uusitalo, Juha E. Peltonen and Yorck O. Schumacher
The purpose of this research was to evaluate the performances of female middle- and long-distance runners before and after the implementation of a new antidoping strategy (the Athlete Biological Passport [ABP]) in a country accused of systematic doping. A retrospective analysis of the results of Russian National Championships from 2008 to 2017 was performed. The 8 best female performances for the 800-m, 1500-m, 3000-m steeplechase, 5000-m, and 10,000-m events from the semifinals and finals were analyzed. The yearly number of athletes fulfilling standard qualifications for international competitions was also evaluated. Overall, numbers of athletes banned for doping in 2008–2017 were calculated. As a result, 4 events (800, 1500, 5000 [all P < .001], and 10,000 m [P < .01]) out of 5 showed statistically significant deterioration in the performances when comparing before and after the introduction of the ABP. The 3000-m steeplechase was the only event that did not show statistically significant change. The highest relative decrease in the number of runners who met standard qualification for international competition was for the 5000-m event (46%), followed by 1500-m (42%), 800-m (38%), 10,000-m (17%), and 3000-m steeplechase (1%). In conclusion, implementation of the ABP was followed by a significant reduction in the performance of female runners in a country accused of systematic doping. It can be reasonably speculated that more stringent antidoping testing, more specifically the introduction of the ABP, is a key reason for this reduction.
Dean Barker, Gunn Nyberg and Hakan Larsson
Purpose: To describe student learning when physical education teacher and students attempted to develop movement capability. Methods: The study reports on the implementation of a 10-lesson pedagogical sequence. Data were generated using observations, interviews, and student diaries with one grade 9 class (26 students aged approximately 15 years) as they developed juggling capabilities. Data were analyzed using the notion of corporeal thresholds. Results: Results show that (a) a “throw–throw–catch–catch” pattern emerged as a corporeal threshold for juggling within the sequence; (b) most learners had crossed the threshold at the outset and were able to experiment with different forms of juggling during the sequence; (c) some students crossed the threshold during the sequence. These students experienced liminal phases, characterized by frustration and an initial feeling that they were juggling in the “wrong” way; and (d) some learners became stuck, pretended to know what to do, and did not cross the threshold during the 10 lessons. Discussion/Conclusion: Three issues related to the threshold approach are discussed: student identity and group membership, the process of learning, and the emotional dimensions of movement learning. This study is concluded with reflections on the implications of the results for scholarship.
Michal Botek, Jakub Krejčí, Andrew J. McKune and Barbora Sládečková
Purpose: Hydrogen-rich water (HRW) has been shown to have an antifatigue effect. This study assessed up-hill running performance, as well as physiological and perceptual responses after supplementation with 1680 mL HRW between 24 h and 40 min before running, in athletes of heterogeneous running ability. Methods: Sixteen males (mean [SD] age 31.6 [8.6] y, VO2max 57.2 [8.9] mL·kg−1·min−1, body fat 13.4% [4.4%]) participated in this study. Using a randomized, double-blind, placebo-controlled crossover design, participants consumed either HRW or placebo prior to performing two 4.2-km up-hill races separated by a week. Race time (RT), average race heart rate, and immediately postrace rating of perceived exertion were assessed. Results: After analysis of data for all runners, HRW effect was unclear (−10 to 7 s, 90% confidence interval) for RT, likely trivial for heart rate (−2 to 3 beats·min−1), and likely trivial for postrace rating of perceived exertion (−0.1 to 1.0). A possible negative correlation was found between RT differences and average RT (r = −.79 to −.15). HRW for the 4 slowest runners (RT = 1490  s) likely improved the RT (−36 to −3 s), whereas for the 4 fastest runners (RT = 1069  s) the performance effect of HRW was unclear (−10 to 26 s). Conclusions: HRW intake had an unclear antifatigue effect on performance in terms of mean group values. However, it appears that the magnitude of the antifatigue effect of HRW on performance depends on individual running ability.