Keith Baar, (Baar 2014)
Follow these guidelines to avoid the downsides of Concurrent training:
- “Any high-intensity endurance training sessions should be performed early in the day. Then, a period of recovery of at least 3 [hours] should be given [before resistance training].”
- “Resistance exercise should be supported by readily digestible, leucine-rich protein as soon as possible after training […]”
- “Fully refuel between the morning high-intensity endurance training session and the afternoon strength session […]”
- “To improve the endurance response to lower-intensity endurance training sessions and provide a strong strength stimulus, consider performing strength training immediately after low-intensity, non-depleting, endurance sessions.”
I’ve integrated this into my Exercise program.
Very few sports use only endurance or strength. Outside of running long distances on a flat surface and power-lifting, practically all sports require some combi- nation of endurance and strength. Endurance and strength can be developed simultaneously to some degree. How- ever, the development of a high level of endurance seems to prohibit the development or maintenance of muscle mass and strength. This interaction between endurance and strength is called the concurrent training effect. This review specifically defines the concurrent training effect, discusses the potential molecular mechanisms underlying this effect, and proposes strategies to maximize strength and endurance in the high-level athlete.
The concurrent training effect on strength. The figure shows the increase in one repetition maximum in the squat in subjects who participated in 10 weeks of high-intensity resistance exercise alone (resistance), endurance exercise alone (endurance), and both types of training (concurrent). Also, note that the strength and concurrent groups both increased their strength together up to 7 weeks, when the strength group started making greater gains than the concurrent group (adapted from Hickson , with permission). 1RM one repetition maximum
Molecular underpinning of muscle hypertrophy
Increased strength is the combined effect of improvements in neural activation, muscle fiber size, and connective tissue stiffness. Therefore, concomitant endurance exercise could decrease adaptations of any/all of these physiological parameters. There does not appear to be a decrease in the neural (learning) adaptation […] no one has measured the effect of concurrent training on connective tissue stiffness, so we are unsure of the role of this tissue in the impaired strength response. […] the primary effect of endurance exercise seems to be a decrease in resistance exercise-induced muscle hypertrophy.
Science-based recommendations for training to maximize concurrent training
Using the molecular information provided in Sects. 2–5, some simple nutritional and training strategies can be devised to maximize the adaptations to concurrent training. The goal of these recommendations is to maximize the mitochondrial adaptation to endurance exercise and the muscle mass and strength adaptation to strength training. To do this, the following could be recommended:
- Any high-intensity endurance training sessions should be performed early in the day. Then, a period of recovery of at least 3 [hours] should be given, so that AMPK and SIRT1 activity can return to baseline levels, before resistance exercise is performed. This suggestion is based on the fact that AMPK activity increases rapidly and then returns to baseline levels within the first 3 [hours] after high-intensity exercise , whereas mTORC1 activity can be maintained for at least 18 h after resistance exercise [8, 9].
- Resistance exercise should be supported by readily digestible, leucine-rich protein as soon as possible after training to maximize leucine uptake , mTOR recruitment to the lysosome , and protein synthesis . Since, in this scenario, resistance exercise is performed later in the day, it becomes even more important to also consume protein immediately prior to sleep to maximize the synthetic response overnight .
- Fully refuel between the morning high-intensity endurance training session and the afternoon strength session since AMPK can be activated by low glycogen , and SIRT1 is activated by caloric restriction . If it is not possible to refuel completely because of the training volume and intensity, it might be best to reserve a portion of the offseason (and short periods in season) exclusively for increasing muscle size and strength and then use higher dietary protein intakes to maintain that muscle mass as the aerobic load increases through the season .
- To improve the endurance response to lower-intensity endurance training sessions and provide a strong strength stimulus, consider performing strength training immediately after low-intensity, non-depleting, endurance sessions. Performing a strength session immediately after a low-intensity endurance session results in a greater stimulus for endurance adaptation than the low-intensity endurance session alone  and the low-intensity session will not affect signaling pathways regulating strength gains [51–53].