Beth W. Glace

Central Fatigue after Cycling Evaluated Using Peripheral Magnetic Stimulation

UNLABELLED Central and peripheral mechanisms contribute to fatigue during exercise. Electrical and transcranial magnetic stimulation have been used to assess these fatigue mechanisms. Peripheral magnetic stimulation (PMS) of the femoral nerve is associated with very little subject discomfort and has been shown to elicit quadriceps contractions of >70% maximal voluntary contraction (MVC). PURPOSE To examine peripheral versus central mechanisms of fatigue in men during prolonged cycling using a peripheral nerve magnetic stimulation-based technique. METHODS Eleven men (aged 41 +/- 3 yr) cycled for 2 h at approximately 66% of VO2peak (55 +/- 2 mL x kg(-1) x min(-1)) with five 1-min sprints interspersed, followed by a 3-km time trial. Oxygen consumption was measured every 20 min to verify a constant workload. RPE were measured simultaneously and during each sprint using a Borg scale. Quadriceps isometric strength testing was performed in a seated position before and after cycling: 1) MVC, 2) MVC with superimposed magnetic stimulation to measure central activation ratio (CAR), 3) femoral nerve stimulation alone. One-minute recoveries were allowed between contractions. Changes in metabolic measurements over time were analyzed with repeated-measures ANOVA, and strength changes before to after with Students paired t-tests. RESULTS HR (P = 0.03) and RPE (P < 0.001) increased over time during the 2 h, and MVC declined by 22% (P = 0.001) indicating fatigue. Force elicited by PMS alone decreased 17% (P < 0.001). CAR decreased from 83% before exercise to 71% (P = 0.005) after exercise indicating a loss of central drive. PMS-induced force was > or =90% of MVC. CONCLUSIONS Results clearly demonstrate that trained cyclists experience significant central fatigue during prolonged cycling. PMS may be a better technique for identifying central fatigue than the traditionally used interpolated twitch technique.

The Effect of Creatine Supplementation on Strength Recovery after Anterior Cruciate Ligament (ACL) Reconstruction: A Randomized, Placebo-Controlled, Double-Blind Trial

Background Creatine supplementation has been shown to augment training-induced strength gains. The purpose of this study was to examine the effect of creatine supplementation on recovery of muscle strength after anterior cruciate ligament (ACL) reconstruction. Hypothesis Creatine supplementation will facilitate strength gains after ACL reconstruction. Study Design Double-blind, prospective, and randomized clinical trial. Methods Sixty patients were randomized into creatine or placebo groups. Quadriceps and hamstring strength and power were measured isokinetically. Hip flexor, abductor, and adductor strengths were measured with a handheld dynamometer prior to surgery and at 6 weeks, 12 weeks, or 6 months after surgery. Results From 6 weeks to 12 weeks after surgery, there were significant increases in strength on the involved side for knee extension (47%), knee flexion (27%), hip flexion (20%), hip abduction (9%), and hip adduction (17%). These strength improvements were unaffected by creatine supplementation with similar effects in the creatine and placebo groups. From 6 weeks to 12 weeks after surgery, there were significant increases in power on the involved side for knee extension (46%) and knee flexion (26%), but these effects were not affected by creatine supplementation. At 6 months, creatine supplementation did not affect outcome as measured by the single leg hop test for distance or the knee outcome score. Conclusions The results demonstrate that patients do not benefit from creatine supplementation during the first 12 weeks of rehabilitation after ACL reconstruction.

Energy Balance and Weight Control (Male and Female)

Evolution in all species is dependent to a large degree on metabolic efficiency. If energy intake does not at least equal energy utilization, growth and reproduction are not possible. Because Homo sapiens have been subjected to these same forces for millions of years, availability of energy will profoundly influence behavior and activity. Environmental and supply factors today make energy surplus a real possibility for most humans. Indeed, unless dietary habits are controlled and physical activity is a steady component of daily life, an energy surfeit is likely. It is estimated that one-third of all Americans are 20% over ideal body weight. This stress is not without effects on multiple hormonal systems in the body. There are situations where energy expenditure exceeds supply, and adjustments to this stress can result in extreme changes in hormone activity and metabolic rate. Alternatively, extreme changes in hormone activity and metabolic rate can cause energy expenditure to exceed supply. Some of these changes are significant threats to normal health and may impact well-being for long periods following the caloric challenge. This chapter attempts to make sense of the current literature addressing the interaction of energy balance and various hormone systems in the body.

BODY DISSATISFACTION IN MEN AND WOMEN PROFESSIONAL BALLET DANCERS

It has been presumed that professional ballet dancers have an increased tendency to develop eating disorders. The Eating Disorder Inventory [EDI] is a widely used self-report scale which measures symptoms of disordered eating. We administered the EDI to male and female professional ballet dancers. 10 eumenorrheic [EU], 7 amenorrheic [AM], and 11 men ballet dancers participated. Anthropometrics were determined during the follicular phase for eumenorrheic women, and surveys were completed and blood was drawn for estradiol and progesterone between days 18–21 of the cycle. Amenorrheic women and men had blood drawn and completed surveys approximately 2 weeks after anthropometric measurements. Mean age was 22 ± 1.6 yrs for men and 22 ± 1.1 yrs for women. Body fat was higher [p < 0.05] for the EU [20%] than for AM [15%] or for men [10%]; body fat of AM did not differ from that of men. Progesterone was greater in EU than AM, 8 vs. 0.57 pg/ml, p = 0.03. 9/10 EU, 9/11 men, but only 3/7 AM women completed the EDI. Higher scores represent an increased likelihood of eating pathology. Scores for male dancers in all sub-categories of the EDI were similar to reference values of non-patient male college students. EU had lower scores than reference non-patient women for Interoceptive Awareness [p = 0.03] and for Impulse Regulation [p = 0.02] with similar scores for Body Dissatisfaction, Bulimia and Drive for Thinness. Additionally, body fat % was correlated to scores for Drive for Thinness and Body Dissatisfaction in EU.

Lack of Energy Conservation in Amenorrheic Ballet Dancers.

1025 Self reported caloric intakes of amenorrheic [AM] dancers have been reported to be less than that of eumenorrheic [EM] dancers. Lower resting metabolic rates [RMR] or decreased thermic effects of food [TEF] might result from caloric restriction. We evaluated RMR and TEF for 3 hours following ingestion of a 500 kcal liquid supplement [Ensure, Abbott Labs] in 5AM and 11 EM dancers. Measurements were made during the early follicular phase in the EM. There was a trend for the AM to weigh less than EM [48.8±3.1 vs 55.9±2.0 kg, p=0.067]. Percent body fat was less in the AM[13±1.4%] compared to EM [20±1.8%], p=0.02, as determined by bioelectrical impedance [RJL Systems] and skin fold measures [Jackson and Pollock]. The decreased RMR in AM disappeared when corrected for lean mass. Table Graphic Table. No caption available. MANOVA revealed no differences between groups nor any interaction of group x time for TEF. Therefore, RMR and TEF of AM and EM dancers was similar after adjusting for lean body mass. Perhaps the discrepancies between reported intakes and caloric expenditures in AM ballet dancers is due to underreporting of food intake or to other mechanisms of energy conservation. file:///C|/Documents%20and%20Settings/User/My%20D...%20Volume%2030(5)%20Supplement_May%201998_180.htm (1 of 2)5/13/2005 10:46:53 AM Ovid: Glace: Med Sci Sports Exerc, Volume 30(5) Supplement.May 1998.180 Section Description American College of Sports Medicine 45th Annual Meeting; June 3-6, 1998; Orange County Convention Center; Orlando, Florida E-16 FREE COMMUNICATION/SLIDE PRES DISORD EAT Accession Number: 00005768-199805001-01026 Copyright (c) 2000-2005 Ovid Technologies, Inc. Version: rel9.3.0, SourceID 1.10284.1.251 file:///C|/Documents%20and%20Settings/User/My%20D...%20Volume%2030(5)%20Supplement_May%201998_180.htm (2 of 2)5/13/2005 10:46:53 AM