123 A Christian Guide to Body Stewardship, Diet and Exercise Lactate threshold (LT) is the point in exercise at which lactate starts to accumulate in the blood above resting levels. Many researchers believe lactate threshold to be a better predictor of cardiovascular fitness than VO2max (Haff & Triplett, 2016). An individual’s LT defines the upper limit of a sustainable pace that can be maintained during training and/or competition. After blood lactate starts to accumulate above resting levels, it becomes impossible for the body to sustain that pace thereby resulting in fatigue. Running at paces below LT will allow the body to reach a steady state in which lactate production no longer increases and remains relatively stable. Ideally, athletes would be able to find and run at their maximal lactate steady state (MLSS) as this would allow them to run at the fastest possible pace without causing fatigue. Ironically, athletes with the same VO2max can have significant differences in their lactate threshold. For example, assume we have two athletes preparing for a 1-mile run and both have the same or similar VO2max scores. However, the LT for the first athlete occurs at 70% of their VO2max; whereas, the LT for the second athlete occurs at 60% of their VO2max. Because the first athlete is able to run at and sustain a pace at higher percentage of their VO2max, he/she will be able to run 1.0-mile faster than the second athlete. In untrained individuals, LT generally occurs around 60-70% of their VO2max. In well-trained endurance athletes, LT generally occurs around 75-80% of their VO2max. In elite endurance athletes, LT can occur at 90% or more of their VO2max (McCormick, n.d.). Recommendations for increasing LT include high-intensity interval training and/or interval training 1-2 times per week as well as pace / tempo training 1-2 times per week (Haff & Triplett, 2016). Exercise economy is the amount of energy required to maintain a consistent pace. Although not to the same extent as VO2max or LT, research suggests exercise economy to be another important factor in predicting endurance performance and may explain some of the performance differences between individuals (Peterson & Rittenhouse, 2019). Some of the factors that influence exercise economy include neuromuscular coordination, muscle fiber type, joint stability, and flexibility (Training 4 Endurance, 2017). Recommendations for improving exercise economy include regular participation in drills aimed at improving overall run technique (e.g., skipping, bounding, double and single-leg hops, sprinting). Other recommendations include lower body resistance and plyometric training, especially single-leg exercises (e.g., Bulgarian split squats, lunges), as well as exercises aimed at strengthening the torso (e.g., plank, side plank, back hyperextensions). Muscle fiber type is another, albeit small, factor that can influence endurance performance. Individuals with higher percentages of slow-twitch (type I) muscle fibers tend to perform better at slower, longer endurance events (e.g., 5-km, 10-km, ½ marathon, marathon); whereas individuals with higher percentages of fast-twitch (type II) muscle fibers tend to perform better at faster, shorter endurance events (e.g., 100-m, 200-m, 400-m, 800-m). Although the majority of slowtwitch muscle fibers seem to be set at birth, a small percentage of fast-twitch fibers can become more aerobic in nature with chronic endurance training (a process called fiber type transition). Figure 6.2 depicts the differences in muscle fiber type percentages for long, middle, and short distance endurance athletes. The red cells represent slow-twitch (type I) muscle fibers; whereas, the white cells represent fast-twitch (type II) muscle fibers.
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