It has been previously reported (6,11,14,22) that aerobic capacity is determined by 3 factors, maximal oxygen uptake (V̇o2max), lactate threshold (LT), and running economy (RE), and that a change in any of these variables will affect performance. Therefore, for sports that largely depend on this component of fitness, knowledge of how best to train aerobic capacity and target its individual factors is essential. The aim of this article, therefore, is to briefly discuss the associated training protocols (high-intensity interval, strength and power, and volume load training) and thus make recommendations based on the evidence herein.
HIGH-INTENSITY INTERVAL TRAINING INCREASES V̇o2MAX AND LACTATE THRESHOLD?
Although the most common method to enhance aerobic capacity is often considered to be via long-distance running at a moderate intensity, this may not actually be most effective. For example, in a group of 55 moderately trained male subjects (averaging 25 years, training 3 times/wk, and an average V̇o2max of 58 mL/kg/min), Helgerud et al. (13) found that high-intensity endurance training is significantly more effective than moderate- and low-intensity training in improving V̇o2max (Table 1) and that intensity and volume of training are not interchangeable. This is in agreement with several other studies (7,15), including those examining athletes with an already high V̇o2max (13) and indeed with those concluding that intensity of training cannot be compensated for by longer duration (28,34).
Interestingly, and in line with 3 other studies (12,19,22), Helgerud et al. (13) found no change in LT as a %V̇o2max (although all groups significantly improved running velocity at LT by an average of 9.6%) and thus concluded that by virtue of increasing V̇o2max, LT would also increase. Because the LT identifies the onset of anaerobic metabolism, it is thus considered responsible for the %V̇o2max that can be sustained for an extended period and therefore an important component of aerobic performance.
Thus, it may be contended that higher intensities elicit greater improvements in V̇o2max than lower intensities (5,8,13,17,35), with intervals performed at near-max intensity being the most effective (8). It may therefore be recommended that once athletes have undergone sufficient aerobic endurance training (perhaps using the conventional continuous moderate-intensity protocols and whereby a V̇o2max >58 mL/kg/min has been achieved), they should progress onto high-intensity interval training and possibly for purposes of variation, alternate between the exampled 15 × 15 and 4 × 4 methods described in Table 1. To the author's knowledge, it is currently not known whether higher-intensity protocols would elicit greater/faster improvements than low-to-moderate-intensity programs in individuals commencing training from a V̇o2max <58 mL/kg/min.
STRENGTH AND POWER TRAINING INCREASES RUNNING ECONOMY?
It is possible that increases in strength may enhance aerobic endurance performance by decreasing the relative force (%max) applied during the loading phases of ground contact (23,26), thereby leading to a reduced metabolic demand for the same force output and creating a motor unit reserve available for additional work (26). In addition, because increases in strength are often accompanied by increases in power and rate of force development (RFD) (1), there would likely be an increase in blood flow (26) and thus an enhancement of muscle oxygenation and the exchange of substrates/metabolites (20). This may be explained by the fact that fewer motor units will be recruited for a given force output/work rate (26) and because of increases in RFD, thereby reducing contraction time. This will then increase relaxation time when oxygenation and substrate exchange occurs.
Therefore, given the proposed adaptations brought about by strength and power training, it is logical to assume that it exerts its greatest influence on RE. Indeed, this may be evidenced by the study of Storen et al. (27), whereby well-trained long-distance runners completed a heavy strength training protocol for 8 weeks, after which time to exhaustion at maximal aerobic speed increased by 72 seconds or 21.3%. This was despite no changes in body weight, V̇o2max, LT velocity, or LT as %V̇o2max. They therefore attributed this to the noted 5% improvement in RE consequent to the strength training intervention.
The strength and conditioning coach should be cautioned against the common resistance training strategy of shortening the rest interval between sets and exercises under the assumption that this will further enhance the aerobic stimulus. In contrast (16,25), if rest periods are too short (≤30 seconds), loading is likely to be compromised, thereby diminishing gains in strength, power, and RFD (26). In addition, because one of the principal adaptations responsible for these benefits is an increase in the number (and size) of type IIa fibers (with a concomitant decrease in the proportion of type IIx), which have a high glycolytic and oxidative potential and are relatively fatigue resistant, a high load (≥85% 1 repetition maximum [1RM]) is required.
Readers are recommended to the article of Turner (30) for details pertaining to volume load and exercise prescription. Based on this article, Table 2 illustrates a sample of resistance training sessions that may be incorporated within a periodized program. Essentially, the program reflects current approaches within strength and conditioning, whereby power (and RFD) must be trained to enhance sports performance (because most motor skills are force and time dependent). As such, volume load stresses a quality over quantity of repetitions (reps) approach (i.e., low reps, high rest), and the relevant exercises are ballistic in nature, thus capable of high power outputs and RFD. Furthermore, the program recognizes the fundamental relationship between maximum strength and these variables (i.e., strength gains can increase both power and RFD) and therefore looks to both enhance and maintain strength throughout all phases.
It is well understood that RE is significantly influenced by muscle-tendon stiffness (22,32,33), and within the discipline of strength and conditioning, it is largely acknowledged that this “stiffness” is best developed through plyometrics. Readers are directed to the work of Turner and Jeffreys (31) for details pertaining to this. Based on this article, Table 3 illustrates a progression of plyometric drills that should be gradually and logically (i.e., when the athlete is competent at the preceding drill) added to the athlete's resistance training program. Essentially, these drills help accommodate the athlete to high landing forces and gradually inhibit the Golgi tendon organ, which is responsible for muscle compliance, thus enhancing propulsion and economy. These drills will further enhance the athlete's RFD by mimicking the short contraction times and ground contact times produced while running.
VOLUME LOAD TRAINING: TOO MUCH OF A GOOD THING?
It is important to note that strength, power, and plyometric training should not just simply be added to the existing aerobic training schedule. For example, Bastiaans et al. (3) and Paavolainen et al. (21) replaced 37% of total aerobic endurance training time with strength training. This protocol was able to preserve if not enhance the ability to maintain high power outputs, at least for short periods, and thus translate into factors associated with enhanced aerobic endurance performance (based on the 1-hour time trials) (26). Therefore, these studies replaced some of the aerobic endurance training with strength training rather than simply adding to it. It has been shown that high volumes of training can produce a large training stress, thus decreasing the testosterone to cortisol ratio (4,9,10), such that strength and aerobic endurance gains are eventually compromised (26). In summary, these reports also contest the commonly held belief that concurrent strength and aerobic training compromises athletic development. Although this may be true for strength and power athletes, it can be noted that this is not the case for aerobic athletes.
The aerobic capacity is determined by 3 factors: (a) V̇o2max, (b) LT, and (c) RE, and each one should be targeted to optimize aerobic development. It appears that V̇o2max and LT can be adapted simultaneously and may be best trained through high-intensity intervals. Although RE is positively affected by training years (18), proportion of type I fibers (24,29) and anthropometry (2), gains to this component can be exacerbated through resistance training emphasizing high-intensity compound exercises (e.g., squats and deadlifts at ≥85% 1RM) and high power/velocity lifts (ballistic exercises). These should be further supplemented with drills that enhance the stretch-shortening mechanism (i.e., plyometrics), thus facilitating additional improvements in stride propulsion and economy.
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