Search Results

The aim of this review is to provide an up-to-date summary of the evidence surrounding glycemic index (GI) and endurance performance. Athletes are commonly instructed to consume low-GI (LGI) carbohydrate (CHO) before exercise, but this recommendation appears to be based on the results of only a few studies, whereas others have found that the GI of CHO ingested before exercise has no impact on performance. Only 1 study was designed to directly investigate the impact of the GI of CHO ingested during exercise on endurance performance. Although the results indicate that GI is not as important as consuming CHO itself, more research in this area is clearly needed. Initial research investigating the impact of GI on postexercise recovery indicated consuming high-GI (HGI) CHO increased muscle glycogen resynthesis. However, recent studies indicate an interaction between LGI CHO and fat oxidation, which may play a role in enhancing performance in subsequent exercise. Despite the fact that the relationship between GI and sporting performance has been a topic of research for more than 15 yr, there is no consensus on whether consuming CHO of differing GI improves endurance performance. Until further well-designed research is carried out, athletes are encouraged to follow standard recommendations for CHO consumption and let practical issues and individual experience dictate the use of HGI or LGI meals and supplements before, during, and after exercise.

The present study examined the effects of a mental skills training package on competitive gymnasium triathlon performance and evaluated the utilization and impacts of the mental skills during performance. Four participants competed against each other on ten occasions in a single-subject multiple baseline across individuals design, which was used to evaluate an intervention package including goal setting, relaxation, imagery, and self-talk. The results indicated the mental skills package to be effective in enhancing all participants’ competitive triathlon performance and usage of mental skills from baseline to intervention phases. Qualitative data revealed that each of the mental skills were employed both prior to and during each triathlon and had varying impacts depending on when they were utilized. Issues regarding mental skill effectiveness and usage within competitive endurance performance are discussed.

The use of nutritional ergogenic aids containing Eleutherococcus senticosus (ES), a plant which is also known as ciwujia or Siberian ginseng, is relatively common among endurance athletes. Eleutherococcus senticosus has been suggested to improve cardiorespiratory fitness (CF) and fat metabolism (FAM) and, therefore, endurance performance (EP). This article reviews the studies that evaluated the effects of ES during endurance exercise, three of which suggest that ES substantially improves CF, FAM, and EP. However, each of these reports contains severe methodological flaws, which seriously threaten their internal validity, thereby rendering hazardous the generalization of the results. On the other hand, 5 studies that used rigorous research protocols show no benefit of ES on CF, FAM, and EP. It is therefore concluded that ES supplementation (up to 1000 to 1200 mg/d for 1 to 6 wk) offers no advantage during exercise ranging in duration from 6 to 120 min.

To determine the effects of depleted iron stores on endurance performance and blood lactate concentration, eight active women with normal (>26 ng/ml) and eight with low (< I2 nglml) plasma ferritin concentrations were studied while performing a ${\text{VO}}_2\max$ and an endurance test (80% ${\text{VO}}_2\max$ ) on a cycle ergometer. The low femtin group had significantly lower serum iron concentration and transferrin saturation and higher TIBC than the normal femtin group. Mean ${\text{VO}}_2\max$ was not significantly different between groups. No significant difference was found in total time to exhaustion during the endurance test for low (23.2 min) and normal (27.0 min) femtin groups; however, the normal femtin group exercised 14% longer. Blood lactate concentrations following the VOzmax and endurance test did not differ significantly between groups. Food diaries revealed lower daily absorbable iron intake by the low femtin group compared to the normal ferritin group. Ferritin concentration was significantly related to absorbable iron (r=.72) and total iron (r=.70) intake. The results suggest that women with depleted iron stores who are not anemic may have less endurance, but do not have higher blood lactate during exercise than women with normal iron stores.

The present investigation tested the interactive effects of goal difficulty and positive reinforcement in the form of verbal persuasion on endurance performance. Two experiments were conducted in laboratory and field settings. In Experiment 1, subjects (n=87) were assigned to a realistic or an unrealistic goal condition and either received or did not receive positive reinforcement while performing the 3-minute sit-up test over the course of 5 weeks. In addition, two control conditions were utilized including a do-your-best group and a no-treatment control group. Results indicated no significant main or interaction effects for the goal setting or positive reinforcement conditions. In Experiment 2, subjects (n=120) squeezed a hand dynamometer for as long as they could. Experimental conditions were similar to those in Experiment 1 except that the verbal persuasion was individualized since it was group oriented in the first experiment. Results again indicated no significant between-subjects main effects or interactions. Questionnaires revealed that subjects accepted their assigned goals, tried extremely hard, were committed to achieving their goals, and felt their goals were important. Results are discussed in terms of the goal attainability notion (Garland, 1983) and self-efficacy theory (Bandura, 1977). Future directions for research are offered.

Endurance athletes commonly ingest caffeine as a means to enhance training intensity and competitive performance. A widely-used source of caffeine is coffee, however conflicting evidence exists regarding the efficacy of coffee in improving endurance performance. In this context, the aims of this evidence-based review were threefold: 1) to evaluate the effects of preexercise coffee on endurance performance, 2) to evaluate the effects of coffee on perceived exertion during endurance performance, and 3) to translate the research into usable information for athletes to make an informed decision regarding the intake of caffeine via coffee as a potential ergogenic aid. Searches of three major databases were performed using terms caffeine and coffee, or coffee-caffeine, and endurance, or aerobic. Included studies (n = 9) evaluated the effects of caffeinated coffee on human subjects, provided the caffeine dose administered, administered caffeine ≥ 45 min before testing, and included a measure of endurance performance (e.g., time trial). Significant improvements in endurance performance were observed in five of nine studies, which were on average 24.2% over controls for time to exhaustion trials, and 3.1% for time to completion trials. Three of six studies found that coffee reduced perceived exertion during performance measures significantly more than control conditions (p < .05). Based on the reviewed studies there is moderate evidence supporting the use of coffee as an ergogenic aid to improve performance in endurance cycling and running. Coffee providing 3–8.1 mg/kg (1.36–3.68 mg/lb) of caffeine may be used as a safe alternative to anhydrous caffeine to improve endurance performance.