Physical Activity

The Science Behind Cross Training

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These days we hear a lot about “cross training,” but what exactly is it? Cross training simply involves performing athletic training in another discipline in order to improve at your main sport. For example, using weightlifting to improve your performance in football, gymnastics or middle distance running is an example of cross training. The fundamental idea behind cross training is to improve in all five accepted aspects of fitness: cardiovascular endurance, muscular strength, muscular endurance, flexibility and body composition.

Training specifically in just one sport often improves some of these dimensions of fitness but very rarely improves all of them. However, some experts believe that by cross training — which typically involves performing a wide range of movements — all five of these aspects of fitness will get better.

The Science Behind Cross Training

There are several studies looking at the effects of cross training, often focused on the effects of cross training on running performance. A study published in 1994, for example, highlighted the benefits of cross training. It concluded that cross training provides a particular benefit to an athlete recovering from injury or when an athlete has overtrained (1).

Indeed, running causes a huge number of injuries with as many as 56% of runners each year experiencing problems. Overall, this equates to between 2.5 and 12.1 injuries per 1000 hours of running (2). Data on injuries in runners suggests strongly that the only way back to good health is to cut out the running and take up something else in order to maintain your level of fitness.

To prevent, for example, overuse injuries you can change your daily routines. An analysis known as the functional movement screen (FMS) of NFL players identified that those with physical asymmetries were, unsurprisingly, at greater risk of injury than those who possessed greater symmetry (3). Think, for instance, of a baseball player whose day-to-day activity involves the repeated use of a single batting arm. Or the tennis player using the same arm for serving or both hands to play a backhand. This pattern of overuse is recognized by the American Orthopedic Society for Sports Medicine, which encourage athletes to use cross training to prevent such injuries.

Interestingly, the benefits of cross training aren’t just physical. Cross training, by exploiting the use of different stimuli, can also overcome psychological or mental/emotional fatigue associated with training in just one sport. Traditionally, the off-season is the perfect opportunity to engage in some cross training. During this time, athletes can reduce the physical and psychological pressures of their sport while maintaining their level of fitness. It also provides an opportunity for teams to train differently in a social, less competitive setting and improve team bonding.

The Importance of Weightlifting

Some research suggests that cross training doesn’t provide much benefit unless it involves resistance weight training. Dr. Hirofumi Tanaka, an exercise physiologist at the University of Texas, identified that resistance training improved endurance in running and cycling in trained and untrained athletes, though this effect was not demonstrated in swimmers (4).

While endurance activities (running, cycling, swimming) change the activity of glycolytic enzymes (enzymes used for breaking down glucose), increasing energy storage in the muscle and increasing the density of mitochondria (cellular powerhouses), strength training reduces mitochondrial density, while marginally impacting capillary density, metabolic enzyme activities and intramuscular substrate stores. It boils down to the fact that endurance training and strength training have opposite physiological effects.

“As a result, endurance training facilitates aerobic processes, whereas resistance training increases muscular strength and anaerobic power.”

Additionally, these two types of training have an opposite effect on muscle fiber size (resistance training increases while endurance training decreases the size of muscle). As a result, endurance training facilitates aerobic processes, whereas resistance training increases muscular strength and anaerobic power. This means if you want to be an all-round athlete you should train using both modalities as this will allow you to benefit from both metabolic sources in performance.

So, the takeaway message here is don’t leave it until you have an injury before you start cross training. Incorporate different activities, in particular weightlifting, as part of your training routine. That way you’ll not only have fewer injuries but you’ll also benefit psychologically.


  1. “Effects of cross-training.” Hirofumi Tanaka. 1994.
  2. “Running injuries.” Willem van Mechelen. 1992.
  3. “Can serious injury in professional football be predicted by a preseason functional movement screen.” Kyle Kiesel, et al. 2007.
  4. “Impact of Resistance Training on Endurance Performance.” Dr. Hirofumi Tanaka, Thomas Swensen. 1998.