Strength and endurance training compliment each other for superior athletic performance. Resistance training increases strength limits, muscle mass, bone density and neuromuscular coordination. Cardiorespiratory exercise improves endurance capacity and blood circulation, while making it easier to maintain a healthy body weight. The two training methods draw from different energy pathways, and have few overlapping effects in the body. Problems can arise with concurrent training programs – especially in maximizing strength development.
Strength training recruits anaerobic energy systems, wherein creatine phosphate and lactic acid provide the main sources for fuel in the absence of oxygen. Programs using progressive overloads train a person above their lactate threshold, a level at which lactic acid is produced faster than it is removed. This byproduct of anaerobic exercise causes muscles to temporarily lose their ability to contract against resistance. Anaerobic metabolism is not sufficient for sustained activities – it’s best for short burst of force – but it can be improved through resistance training for increases in limit strength and muscle mass. This energy pathway is essential in sprinting, gymnastics and weight lifting.
Endurance training draws heavily on aerobic metabolism, an energy system that requires the presence of oxygen. Activities lasting longer than 30 seconds start to pull from aerobic energy pathways. This oxidative system has a low rate of energy output, but it can sustain activity much longer than the more powerful anaerobic pathways. Maximal oxygen uptake, or VO2 max, is highly trainable through regular exercise. Strong aerobic fitness is a requirement for long-distance running and swimming.
Strength and endurance training produce widely diversified adaptations in the body; as such, they require significantly different approaches to exercise prescription. Robert C. Hickson first revealed the concurrent training phenomenon in 1980, which opened the flood doors of interest for further investigations. Subsequently, many early studies were against any concurrent training. Linear periodization routines, alternating training cycles from one element to the other, became exceedingly popular.
In December 1999, researchers from the Centre for Sports and Exercise Science in New Zealand published a study demonstrating that endurance training inhibits strength development when compared to strength training alone. They hypothesized that skeletal muscle cannot adapt metabolically or morphologically to both strength and endurance training simultaneously.
In March 2000, continued research was published by the Faculty of Physical Education and Recreation at the University of Alberta, Canada. Their findings supported the contention that combined strength and endurance training can suppress positive adaptations to strength training. This effect is largely influenced by increased secretion of cortisol, the body’s natural stress-fighting and anti-inflammatory hormone. Elevated cortisol levels put the brakes on muscular development by promoting protein breakdown.
Two years later, a study published in March 2002 contradicted recent reports. Researchers from the Department of Orthopedics, University of Wisconsin-Madison, demonstrated that concurrent performance of both strength and endurance training does not impair adaptations in strength, muscle hypertrophy and neural activation. However, their research was based on 30 sedentary male subjects. Concurrent training’s negative impact is less obvious in individuals unaccustomed to regular exercise. This is likely due to a greater potential for improvement.
In March 2003, research was published by the Neuromuscular Research Center in Finland. It was demonstrated that even low-frequency strength and endurance training leads to interference in explosive strength development in conditioned muscles. This was mediated in part by the limitations of rapid voluntary neural activation.
In July 2008, researchers from Tunisia and Australia published a study examining the effects of concurrent endurance and circuit resistance training on muscular strength and power development. The aim was to determine the influence of intrasession sequencing. According to the authors, the order for endurance and resistance exercise during a workout did not alter the fact that increases in strength and power are significantly greater in those performing resistance training only. Decreasing workout frequency can improve strength gains but resistance training alone, without concurrent endurance training, seems to be the best option. In other words, goal-orientated training, using periodization techniques, continues to prevail.
As fitness levels increase, more specificity must be injected into exercise prescription. When increased muscle size and strength is most important, avoid a lot of concurrent endurance training. Efforts focused on improving aerobic fitness should only be augmented by attempts to maintain strength levels – in order to preserve muscle mass, avoid sports injuries and improve neuromuscular coordination.
If an athlete is already taxed by heavy training demands, then any additional activity, of any kind, won’t be of benefit. Symptoms of overtraining syndrome can hamper both strength and endurance performance. Ultimately, the way you train should be based on your goals, fitness level, personal abilities and environment.
Chtara M, Chaouachi A, Levin GT, Chaouachi M, Chamari K, Amri M, Laursen PB. Effect of Concurrent Endurance and Circuit Resistance Training Sequence on Muscular Strength and Power Development. Journal of Strength & Conditioning Research. 22(4):1037-1045, July 2008.