Concurrent training is a combination of cardio and resistance training in the same session. Many believe it can achieve multiple goals, but does it?

This article is adapted from Timing Resistance Training by Amy Ashmore.

Concurrent training is doing cardiovascular endurance and resistance training within the same session or closely together within the same day. Long ago in the exercise science world, concurrent training was promoted as a way to save time while reaching multiple training goals.

More recently, however, it’s clear that the mechanisms of cardiovascular endurance training and resistance training compete with one another at the molecular level. Under certain situations, they can cancel each other out. This essentially renders significant muscle strength and power outcomes nonexistent.

Concurrent Training – Not for Strength!

The original landmark study on concurrent training outcomes (12) showed that muscle strength actually decreased during the last 2 weeks of a concurrent training study period in which the subjects did both cardiovascular endurance and resistance training.

These results were significant because they showed that cardiovascular training ceased upper-end strength improvements while leaving cardiovascular endurance, as measured by VO2max, unaffected.

Since 1980, the message has been that cardiovascular endurance training interferes with muscle strength performance and that the body tends to favour cardiovascular endurance outcomes over muscle strength outcomes.

Muscle Confusion

Concurrent training causes muscle confusion at the molecular level. Consider this: Muscles get confused just like you do. If you walk into a spin centre ready for a spin class only to find Pilates equipment on the floor, you get confused. Muscles are the same way. When two competing kinds of exercise, such as cardiovascular endurance training and resistance training, are performed during the same workout session, the involved muscles become confused.

Ashmore goes on to explain that muscle confusion occurs at a molecular level; the molecular mechanisms associated with cardiovascular endurance and muscle strength and power are different. When the two modes of training occur too close in time, muscles simply don’t know what to do. In the end, the molecular mechanisms associated with muscle strength and power performance are sacrificed at the expense of cardiovascular endurance goals, and results are diminished.

HIIT and Strength

In one study on concurrent training using contemporary popular training methods (8), researchers studied a combination of high-intensity interval cycling endurance training and high-velocity (or speed) resistance training.

The results showed that cycling VO2max increased to the same extent in both the endurance training only group and the combined endurance and resistance training group. Results were measured several times over the 7-week period, however, strength improvements were different in each group.

The resistance training only group had increases in maximal torque (the rotary component of force output) whereas the endurance with the resistance training group had a significant improvement only at specific torques. This suggests that the interference in strength and power development occurred at high- but not low-velocity rates of force production.

Split Body Concurrent Training

Additional evidence suggests concurrent cardiovascular endurance training interferes with increases in muscle size (15) and thus interferes with strength development. Researchers found that combining cardiovascular endurance and resistance training negatively affected fibre cross-sectional areas. However, in this particular study, the authors found that concurrent training compromised strength development only when both modes of exercise engaged the same muscle group, suggesting a local effect rather than a systemic one.

Subsequent studies show something different about local versus systematic effects of concurrent training. One study examined the effects of lower-body sprint interval training on upper-body hypertrophy and strength (14). The results showed that sprint interval training combined with resistance training adversely affected upper-body hypertrophy and strength. This finding is significant because it is counter to earlier research suggesting a local effect of concurrent training.

The study showed that the effects of concurrent aerobic endurance and resistance training are not muscle-use specific. Lower-body sprint interval training adversely affected upper-body strength performance; therefore, the effects of endurance training affect nonworking muscles. This is significant in concurrent programming in which most modes of cardiovascular endurance training use the lower body.

It appears based on this study that the upper-body muscles are not spared the negative consequences of concurrent training and interference, even when not used. The results suggest that the mechanisms responsible for interference cannot be avoided by working different muscle groups during cardiovascular endurance and resistance training.

Competing Mechanisms

In one study, researchers measured Muscle force generation capacity (MFGC) over a 4-day test period combining high-intensity, lower-body resistance training with cardiovascular endurance training (7).

Unfortunately, the results showed that strength was diminished over the test period when resistance training and cardiovascular endurance training were done in the same session, demonstrating interference.

The results clearly indicated that the mechanisms that cause muscle growth, strength and power outcomes and those associated with cardiovascular endurance changes compete and interfere with one another and reduce the quality of resistance training sessions.

Neural Factors

Another study compared the neuromuscular adaptations between same-session combined resistance and cardiovascular endurance training (cycling) with two loading orders and different-day combined training over 24 weeks (9). Researchers divided 56 subjects into three training groups:

• different-day combined resistance
• cardiovascular endurance training 4 to 6 days per week
• same-session combined training in which cardiovascular endurance preceded resistance training or vice versa 2 or 3 days per week.

Researchers measured and analysed:

• dynamic and isometric resistance
• muscle activity
• voluntary muscle activation
• muscle cross-sectional area
• cardiovascular endurance performance.

The results found that all groups showed improved performance on dynamic 1RM and isometric force. There were also improvements in muscle cross-sectional area and maximal power output during cycling.

The different-day and resistance training before cardiovascular training groups showed increased voluntary activation during training. In the cardiovascular training before resistance training group, there was no increase in voluntary activation detected after 12 or 24 weeks.

Cardio before resistance?

Other results showed that cardiovascular training before resistance training resulted in no improvement in muscle activity in isometric maximal contractions. The resistance before cardiovascular group showed increased maximum muscle activity after 24 weeks during maximal isometric muscle actions. This is important because it shows increased neural activity in the resistance training before cardiovascular exercise group and no improvements in neural activation for the cardiovascular before resistance training group. Furthermore, neural adaptations showed indications of being compromised when cardiovascular training was performed before resistance training.

In the book, Timing Resistance Training there are more examples fo this with recreational endurance runners and leg strength. Ashmore also discusses morning to evening same-session concurrent resistance and cardiovascular endurance training on neuromuscular and endurance performance.

Overtraining

Another reason the mechanisms of cardiovascular and resistance training may compete is simply overtraining. Concurrent resistance and cardiovascular endurance training may lead to overtraining, which can account for the inability of the muscle to attain optimal strength performance (3). In general, overtraining is caused by an imbalance between training and recovery (16), defined by either no improvement or a decline in performance. For example, one study on concurrent training study showed that strength declined in the 9th and 10th weeks of concurrent training (12). The argument was made that the decline in strength was specifically due to overtraining because the concurrent training group did 80 min of training, and the volume of training negatively affected strength development. The muscles were too fatigued to produce adequate force for strength improvements.

However, where strength decrements were found during weeks 9 and 10 of the concurrent training programme, measures of cardiovascular endurance work showed no negative effects of fatigue on endurance from concurrent training, again suggesting that the effects of concurrent training preferentially affect strength development.

Summary

Concurrent training is the use of multiple modes of exercises in a training programme over time to achieve multiple goals that typically include increasing cardiovascular fitness along with muscle hypertrophy, strength and power. However, both historical and contemporary data continues to expose the reality that cardiovascular and resistance modes of training compete with one another at a molecular level. There is a preferential tendency to cancel out muscle hypertrophy, strength and power improvements to salvage cardiovascular fitness.

Although concurrent training does not look promising for sports, athletics and elite fitness, there are some solutions. These lie in strategic programming using the latest research and programming strategies to avoid muscle confusion and interference. Examples of which can be found in Timing Resistance Training.

The decision to include concurrent training in any programme depends on programming goals and individual preferences. It is also important to consider whether muscle hypertrophy, strength and power goals prevail over cardiovascular goals.

This article provides a small snippet of Amy Ashmore’s work. Inside Timing Resistance Training you’ll find more on concurrent training including nutrition, testosterone, cortisol, molecular signalling and more.

References

3. Chromiak J, Mulvaney D. The effects of combined strength and endurance training on strength development. J Appl Sports Sci Res. 1990;4:55-60.

7. Doma K, Deakin G. The cumulative effects of strength and endurance training sessions on muscle force generation capacity over four days. J Aust Strength Cond. 2013;21(suppl 1):34-38.

8. Dudley GA, Djamil R. Incompatibility of endurance and strength-training modes of exercise. J Appl Physiol. 1985;59:1446-1451.

9. Eklund D, Pulverenti T, Bankers S, et al. Neuromuscular adaptations to different modes of combined strength and endurance training. Int J Sports Med. 2014;36:120-129.

12. Hickson RC Interference of strength development by simultaneously training for strength and endurance. Eur J Appl Physiol Occup Physiol. 1980;45:255-263.

14. Kikuchi N, Yoshida S, Okuyama M, Nakazato K. The effect of high-intensity interval cycling sprints subsequent to arm-curl exercise on upper-body muscle strength and hypertrophy. J Strength Cond Res. 2016;30(8):2318-2323.

15. Kraemer WJ., Patton F, Gordon E, et al. Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J Appl Physiol. 1995;78:976-989.

16. Kuipers H, Keizer HA. Overtraining in elite athletes. Review and directions for the future. Sports Med. 1988;6:79-92.

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