• Hot Topic: Energy System Training for Athletes
    Metabolic efficiency training is an often-misapplied concept in the strength and conditioning field. By accurately assessing the time and intensity demands of the sport in question as well as the unique needs of each athlete, coaches can better prescribe conditioning programs that are specific to activity and position. This article covers a brief review of exercise metabolism and applications to training that will increase an athlete’s performance on the field or court.
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  • Figure running across electrocardiogram linesIntroduction

    Multiple training strategies have emerged recently to prepare athletes for competition. The topic of metabolic efficiency has been gaining traction in both the personal training and strength and conditioning world as an additional way for coaches to prepare their athletes for the demands of a particular sport strategically.

    In short, metabolic efficiency, sometimes referred to as energy system development, is a training methodology that helps to better prepare athletes for specific energy demands. Sprinters, for instance, would have different energy demands than distance runners. Although most agree on the end goal, many approach the efficiency through different training avenues. For instance, some advocate the use of sprints and high-intensity work, while others utilize longer duration bouts of exercise.

    In reality, the type of conditioning work should largely be based on the demands of the sport and the individual athlete. To expound upon this topic further, we must first briefly revisit the energy system pathways at work during exercise.

    During an activity, three primary energy systems contribute at different levels depending on intensity (3). The phosphocreatine system contributes the bulk of energy for high-intensity bouts ranging from 1–15 s in length. The glycolytic system continues as the dominant source of fuel from 15 s all the way up to 2 – 3 min in length. Finally, the aerobic system provides energy for anything beyond 3 min.

    Figure 1 
    Figure 1. Energy Production 
     
    As illustrated in Figure 1, all three systems constantly contribute to energy production at some level (3). However, what is more complicated is that certain energy systems are more prevalent than others at specific intensity levels.  

    In its simplest form, energy system training maximizes the efficiency of the dominant system at work during the sport in question. As illustrated above, the contribution of energy from each system is complex. In order to plan a beneficial training program accurately, we must first assess the demands of the particular sport in question. That information should then be applied to the training regimen for the best possible results.


    Nonlinear speedAssessing the Energy Demands of the Sport

    There are three main factors to consider when assessing the metabolic demands of the particular sport in question. The first is the duration of activity. As illustrated in Figure 1, as exercise duration increases, athletes rely more and more on fat metabolism for energy (4).  
     
    As such, proper training should encourage maximal fat metabolism to spare carbohydrates. From an energy standpoint, this reserves glycogen for intermittent bouts of high-intensity exercise. While fuel utilization can be altered through nutritional interventions, those athletes involved in short duration, high-intensity training may respond differently to modifications in fat and carbohydrate intake than athletes involved in long duration, low-intensity training (6).  
     
    Through incorporating low-intensity workouts (current studies point to intensities of 49–64% of maximal oxygen uptake) both in and out of season, an athlete’s metabolism can become more efficient at utilizing fat for fuel leading to better substrate utilization and carbohydrate sparing in competition (1,5).

    Second, the intensity of the exercise must be examined. Intensity typically goes hand-in-hand with duration. Competition bouts that are short in nature tend to also be rather intense, and vice versa. If the athlete must perform repeated short and explosive bursts of physical activity with small intermittent breaks over the span of the competition, the conditioning work should be adjusted to reflect this. 
     
     
    One factor that should be considered is time between bouts of intense effort. For example, a sport like football may last several hours, but an individual player may only be working for 10–12 s per play followed by a brief recovery period and a subsequent high-intensity bout. These short bouts of work repeated throughout the game are intermixed with long breaks of approximately 5–10 min, depending on the length of drives. As a result, determining the intensity of the activity and prescribing appropriate activities for the intensity of the performance play crucial roles in the conditioning of athletes.

    Lastly, the individual needs of particular athletes must be taken into account. For example, different positions require specific adjustments in conditioning demands. The goalie position in soccer requires a unique subset of skills compared to other players. While goalies are not usually required to run a great deal throughout the game, this position does require long spans of intense focus and concentration mixed with explosive movements both on the ground and in the air. 
     
     
    In contrast, a midfielder is often required to perform both offensive and defensive duties, forcing them to transition quickly back and forth across the field, and thus requiring a large amount of running. As such, goalie and midfielder positions will benefit from different training approaches.

    As illustrated in Figure 1, the duration of activity is not the only factor involved in correctly assessing and prescribing training programs aimed at improving metabolic efficiency for athletes. Both the actual exercises prescribed and intensity of the sport greatly affects performance.


    Application to Training

    Some coaches will take the above information and apply it solely to cardiovascular exercise on the treadmill, bike, or other piece of equipment and the athlete may adapt. However, a scenario where an athlete is capable of improving their energy system conditioning in a setting similar to their performance may be more beneficial from not only a metabolic perspective but also in skill development as it relates to their sport.

    The physical demands of the particular sport and athlete should be considered when prescribing exercise modalities for conditioning. For instance, the soccer goalie needs to be highly conditioned and alert as their position requires little running down the field and relies more heavily on explosive lateral movements. Similarly, a tennis player is constantly moving in a multitude of directions while simultaneously setting their upper body to return the ball. Due to the restricted playing area, a tennis player is not able to move straight forward for any prolonged distance.  
     
    As a result of the unique demands of the position and sport, proper energy system training for both a soccer player and a tennis player should be vastly different. In the goalie example, conditioning should involve both traditional means like field sprints and more position-oriented drills (e.g., continuously fielding balls in a variety of positions at the net). In the tennis example, training may be dominated by footwork drills since lateral and change of direction movements both play an integral part of the performance. Position-oriented drills help to develop specific metabolic adaptations while also improving sport performance and developing muscle memory.

    Conclusion

    Metabolic efficiency training is not a new concept in strength and conditioning. As a tool for increasing performance, it is oftentimes prescribed incorrectly or underutilized in programming. By analyzing the sport and particular position in question, coaches can correctly prescribe anaerobic and aerobic training that has a better carryover effect to athletes’ on-field or on-court performance.  
     
    To do this, coaches must understand the interplay of the energy systems during activity and the many factors that go into analyzing the demands of the sport and prescribing workouts. While generalized cardiovascular training certainly has its place, more sport-specific energy system training leads to higher conditioned athletes that will excel in their particular sport. 
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    About the Author:

    Jeremey DuVall, MS, CPT

    Jeremey DuVall, MS, CPT, received his degrees in Exercise Physiology (BS) and Human Performance (MS) from the University of Florida. His passion and specialty focuses on injury prevention and specific strength development for endurance athletes. He also works closely with metabolic testing to evaluate fuel utilization and effectively prescribe exercise training protocols that maximize glycogen sparing and increase fat oxidation. He currently works hand-in-hand with practitioners as a fitness writer to publish detailed training advice in national publications and dispel popular misconceptions.

    REFERENCES →


    1. Achten, J, and Jeukendrup, AE. Optimizing fat oxidation through exercise and diet. Nutrition 20(7-8): 716-727, 2004.
    2. Brooks, GA, and Mercier, J. Balance of carbohydrate and lipid utilization during exercise: The “crossover” concept. Journal of Applied Physiology 76(6): 2253-2261, 1994.
    3. Holloszy, JO, Kohrt, WM, and Hansen, PA. The regulation of carbohydrate and fat metabolism during and after exercise. Frontiers in Bioscience 15(3): D 1011-1027, 1998.
    4. Gastin, PB. Energy system interaction and relative contribution during maximal exercise. Sports Medicine 31(10): 725-741, 2001.
    5. Jeukendrup, AE, Saris, WHM, and Wagenmakers, AJM. Fat metabolism during exercise: A review - part II: Regulation of metabolism and the effects of training. International Journal of Sports Medicine 19: 293, 1998.
    6. Jeukendrup, AE, Saris, WHM, and Wagenmakers, AJM. Fat metabolism during exercise: A review - part III: Effects of nutritional interventions. International Journal of Sports Medicine 19: 371, 1998.

  • Disclaimer: The National Strength and Conditioning Association (NSCA) encourages the exchange of diverse opinions. The ideas, comments, and materials presented herein do not necessarily reflect the NSCA’s official position on an issue. The NSCA assumes no responsibility for any statements made by authors, whether as fact, opinion, or otherwise. 
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      How does elevation play into the effects of metabolic efficiency? Does an athlete who needs to perform at elevations of 8000-10,000 ft. require a higher aerobic capacity to maintain energy exchange?

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