| dc.description.abstract | Endurance sports, including running, cycling, and swimming, remain popular among recreational athletes in the U.S. and across the world. Many of these athletes compete in local, regional, and national races throughout the year. Their performance in competitions is affected by many factors, including genetics, nutrition, and training. Often, recreational athletes receive conflicting recommendations regarding strategies to optimize performance. Direct-to-consumer genetic testing companies promise to give insights into supposed genetic markers of endurance ability; blogs and social media tout the latest diet strategies to lose weight and perform better; virtual coaches and performance-improvement websites sell training plans with sometimes contradictory training strategies. It remains unclear which of these strategies actually benefit endurance athletes. Therefore, this dissertation examined the effects of genetics, diet composition, and training characteristics on endurance performance in recreational athletes, who often spend a considerable percentage of their disposable income and their time on improving race outcomes. Single-nucleotide polymorphisms (SNPs), variations in a single base pair of a gene, have been proposed to affect physical performance. A SNP in the ACTN3 gene (XX genotype), results in deficiency of a-actinin-3, a structural muscle protein that appears important for explosive movements. Studies in rodents suggest that this deficiency could be beneficial for endurance performance. Yet, few studies in humans have directly assessed the effects of ACTN3 genotype on endurance performance. In our first study, we compared self-reported 1-mile and 5-km running personal records (PR) between participants expressing the three different ACTN3 genotypes. Among women, those with the ACTN3 XX genotype reported faster 1-mile PRs compared to those with the RR and RX genotype. We found no differences between genotypes for 1-mile PRs among men or 5-km PRs among either sex. A long-standing strategy to improve endurance performance is to increase carbohydrate (CHO) availability before and during competition to slow the fatigue process. An opposing approach introduced by researchers, coaches, and athletes, is to increase fat oxidation (FATox) capacities by employing a low-CHO or ketogenic diet (KD). This improved ability for FATox at typical race-intensities would open access to an essentially limitless supply of energy substrates stored in the body as fat. However, studies investigating the effects of KD and high-CHO diets (HC) on endurance performance have found conflicting results. In our second study, participants followed an HC and a KD for two weeks each in a random order. They performed a simulated 30-km cycling time trial (TT) at baseline and following each intervention. Participants’ average power output or endurance performance during the TT was substantially lower following the KD when compared with the HC. Endurance training is the main mechanism to improve general cardiorespiratory fitness and performance in races. Training characteristics include frequency, volume, intensity, and training intensity distribution (TID). TID can be determined by the time spent in the easy (Zone 1), moderate (Zone 2), and hard (Zone 3) training zones. Recently, a polarized TID (time in Z1 > Z3 > Z2) has gained popularity, after research suggested that many elite endurance athletes appear to follow this approach. However, the TID employed by recreational athletes and its association with performance is unknown. In our third study, we analyzed the training characteristics of recreational cyclists and triathletes. We investigated their association with endurance performance as measured by estimated relative critical power (CPrel). In our sample, very few recreational athletes followed a polarized TID. When controlling for age, we found that increased training volume and polarization were positively associated with CPrel. In conclusion, ACTN3 genotype does not appear to have a strong effect on endurance performance. Our results, along with findings from other studies investigating so-called endurance SNPs, suggest that individual genetic markers are not good indicators of endurance performance ability; thus, athletes and coaches should not rely upon direct-to-consumer genetic testing for talent identification and sport selection. Further, based on the results of our second study, the KD appears to decrease endurance performance. While additional research using longer nutrition interventions and different performance measures is needed, it appears that maximizing CHO availability remains the best strategy to improve endurance performance. Finally, we found that few recreational athletes follow a polarized TID despite its potentially beneficial effect on performance. | |
