Four specific training components are implemented within the training programs of endurance athletes. These include high-volume training, threshold training, high-intensity interval training, and polarized training. Polarized training can be viewed as a combination of each of the former three training styles. Training programs such as these rely heavily on the consistent participation by the athlete. In this study, 95% of the training sessions were attended. During the training sessions, the training load (intensity determined by HR zones, duration, and frequency) were matched. The training program lasted 9 weeks involving well-trained male and female athletes.  After review, the polarized training style had the greatest beneficial adaptations for the endurance athletes. HIIT was linked to reductions in body mass. Neither high-volume training or threshold training showed a significant affect on body composition or mass. However, high-volume training was linked to improvements in hemodynamic and metabolic efficiency, particularly in glucose and fat utilization.

Focusing on the individual programs themselves, it’s apparent why a polarized training program would be the most successful. An endurance athlete will need to be prepared to use high-intensity, as well as moderate-intensity exercise during a long-distance event. The major hurdle to an endurance athlete’s success comes in the form of energy availability and force output over an extended workload. Particularly important is the rate of lactic acid removal and the conversion of nutrients into ATP. At the lactate threshold, an intensity level marked by less removal than production of lactic acid, the runner would sense inevitable fatigue and eventual repercussions in performance. Due to the oxygen debt that can accompany higher-intensity exercise, it’s expected that increased intensity from a moderate-intensity workload would cause a lack of lactic acid removal. With the delayed conversion of nutrients into ATP, recycled pyruvate would not adequately satisfy the energy requirements and the skeletal muscle would be unable to continue this power output necessary to maintain speed. There are important adaptations that occur when exercising with HIIT. First, the glycogen availability within the muscles increases. This increase in stored energy can delay fatigue during higher intensity exercise. Secondly, the lactic acid threshold will improve, given that the intensity lasts long enough that the conversion of lactate to glucose through the Cori cycle becomes efficient. However, as experienced within the study, the increased exercise intensity can also cause reductions in body mass. Whether the mass loss was skeletal muscle or fat would have to be established by whether the athlete has proper amounts of carbohydrates during exercise and protein following. An increase in oxygen consumption to account for the oxygen debt experienced during HIIT would lead to increased beta-oxidation of fat as well since the aerobic metabolism has enough time that it can convert fat into energy during rest. However, without proper carbohydrate restoration, the athlete runs the slight risk of converting Glucogenic amino acids into glucose and experiencing subsequent skeletal muscle loss over time. This would diminish overall power output and energy efficiency.

Lactic-acid threshold training would improve clearance of lactate and increase the metabolic efficiency of lactate as an energy source. Especially since marathons and their counterpart variations will eventually require higher intensity sprints or levels of exhaustion that will accumulate lactic acid. High-volume training would also benefit the endurance runner when implemented within a polarized training program. The response to high-volume training would prepare the athlete for the endurance training necessary to complete a lengthy bout of exercise. The alteration of skeletal muscle fibre types could occur due to the high-volume training consisting of moderate-intensity exercise. Training with HIIT was also demonstrated to increase the VO2 peak, which is an important adaptation when working at near-maximal levels of exercise intensity. Threshold training also improves the VO2 peak while increasing the lactate and ventilatory thresholds.

Each of these specific adaptations would be needed within the context of an endurance activity. This is why polarized training, which would introduce each of the training styles to the athlete, would cause the most favorable adaptations. This approach symbolizes that specific adaptations across several areas are necessary for optimal athletic performance. Further, due to the unpredictable nature of adaptation, this gives the athlete the greatest chance of adaptation. Limitations to the study include the use of performance diagnostics (incremental testing and VO2peak ramp protocol) to evaluate the four endurance training interventions. For future research, these performance measurements should include a direct comparison with athletic competition.


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