Endurance training elicits favorable skeletal muscle adaptations such as enhanced muscle blood supply (capillarization), energy usage (mitochondria), and fuel storage capacity. Despite this, a common view among coaches and athletes is that endurance exercise is counterproductive for improving anaerobic strength and power performance. This rationale was popularized in a landmark study by Hickson (5) who found that combined aerobic and anaerobic exercise (concurrent training) blunted strength gains, likely caused by an “interference” within the muscle (4). However, recent research shows this is not always the case (7,8), providing evidence for concurrent training’s potential benefits. Appropriately periodizing endurance exercise within the strength/power athlete’s regimen can augment the aerobic system, enhancing short-term anaerobic training capacity through the ability to recover between bouts without negatively affecting muscular adaptation.
Anaerobic athletes, such as Olympic champion track sprinter Marion Jones and Olympic sprint swimmer Li Zhesi, faced allegations of doping with erythropoietin, a substance commonly used by long-duration endurance athletes to increase the blood’s oxygen-carrying capacity. This begs the question: Why would elite anaerobic athletes take an aerobic performance–enhancing drug? The likely answer is recovery between exercise bouts. Anaerobic athletes rely heavily on a well-developed phosphocreatine (PCr) system to rapidly supply energy for muscle contraction. Because PCr resynthesis is an aerobic process, augmenting the aerobic system (preferably through training) would be beneficial for PCr recovery between intense bouts during heavy exercise (3). Furthermore, endurance training improves buffering capacity (2) and prolongs time to exhaustion by enhancing PCr resynthesis (6) as well as markedly increasing muscle capillarization (9). This would further facilitate the ability to manage anaerobically produced by-products. Regardless of the mechanism, improving aerobic capacity is a beneficial strategy for improving anaerobic performance in elite athletes.
The literature on concurrent training for maximizing muscular adaptations has been contentious because of the “interference effect” of combining anaerobic and aerobic exercise modes in close succession. However, a recent training study by Lundberg et al. (7) showed that resistance and cycling exercise separated by 6 hours of rest did not compromise muscle function and increased whole muscle size more than with resistance exercise alone. Furthermore, adaptation was targeted to fast twitch muscle fibers (5-6 × more powerful than slow twitch) while aerobic capacity of the muscle improved. As long as exercise modes are combined with appropriate rest in between (>6 hours), it appears that concurrent training does not hinder muscle power as previously thought.
The notion that endurance exercise adaptations can improve recovery time between intense exercise bouts has merit. Ultimately, the vigor of one’s training dictates performance and increasing the rate at which an athlete can “go again” will improve the overall volume and quality of training. Because all energy systems operate continuously and synergistically regardless of duration or exercise mode, aerobic metabolism always contributes to energy production (e.g., 20% for a short 30-second sprint) (1). This highlights the importance of a well-balanced training strategy for any performance goal. Incorporating aerobic exercise into an anaerobic training model must be done intelligently by allowing sufficient time between modes, monitoring caloric intake to avoid a catabolic (breakdown) state, and limiting the tendency for overtraining. However, with these potentially confounding effects controlled for, there is certainly a case for including aerobic training with anaerobic athletes.
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Long duration aerobic exercise (AE) is well known for its ability to stimulate numerous adaptations important for exercise performance such as enhanced maximal aerobic capacity, buffering capacity, and muscle capillarization (11). However, high-intensity sprint training (HIT) can yield similar, and in some cases better, adaptions than AE. Recent research has shown that HIT enhances maximal aerobic capacity (7), anaerobic capacity (3,4), ventilatory threshold (8), acid buffering capacity (15), and time to fatigue (9). Importantly, these adaptions occur with less time spent training (minutes per week for HIT compared with hours per week for AE) (4,6). Some research even reports greater gains in [Combining Dot Above]O2max (9), stroke volume (6), substrate utilization (2), and peak power (4) after HIT when compared with AE. These studies highlight the idea that AE is not required to elicit metabolic/cardiovascular adaptations and in some cases may actually be less effective than HIT.
Although most beneficial adaptations of AE are equal to or slightly less than that of HIT, the unique consequences of AE must also be considered before judgment is made. First, the long duration of AE can elevate cortisol, an inflammatory stress-responding hormone that promotes muscle loss and fat storage (12). Consistent AE has specifically been shown to induce protein breakdown (10), leading to a negative protein balance. AE not only increases breakdown but also limits the ability to grow (aka protein synthesis) by activating proteins and genes, which directly inhibit the effectiveness of insulin-like growth factor 1 (5) and testosterone. Finally, the amount of slow-twitch muscle fibers (type I) increase due to chronic AE. Changes in muscle fiber type, combined with a loss of muscle mass, decrease the potential for power production, directly compromising anaerobic exercise performance. Conversely, HIT yields comparable metabolic adaptations while stimulating decreases in overall body fat (3), increases in lean body mass (13), and a conversion to fast-twitch (type IIa) fiber types (1).
It is important to recognize that AE may be an acceptable exercise choice for anaerobic athletes in the right situation (e.g., if used minimally and far away from season). However, as a general statement, the consequences of AE are too detrimental for it to be considered an effective training modality for anaerobic athletes; let alone a necessary one. Anaerobic exercise can elicit positive hormone/molecular responses that AE cannot, while still improving aerobic capacity, V[Combining Dot Above]O2max, and ventilatory threshold; all without a major commitment to training time/volume.