Hickson et al. (1980) conducted one of the first studies dealing with concurrent training and found out that training strength and endurance simultaneously has contradicting characteristics. The study was 10 weeks long and had three training groups: strength training group (S), endurance training group (E) and concurrent training group (S+E). S and E groups did only either strength or endurance exercises and S+E group did all the exercises from the other two groups. Strength increased almost equally in the S and S+E groups for the first 6 weeks, but after that strength increases in S+E group leveled off and eventually started to decline on last two weeks.

Aerobic running and cycling performance (VO2max) increased equally in S+E and E groups. These results go well hand in hand with more recent research on the area. It is more common that endurance training interferes with strength adaptations than vice versa. In this article I’m going to go over few possible reasons behind this so called “interference effect” and how to minimize it to get the most out of your training!

Strength or endurance first?

Concurrent training overall is a very complex subject with a lot of variables such as training order, recovery time between exercises and the modality of training. Thus, researching the subject isn’t simple. If we first consider the order of training, Murlasits et al. (2018) found in their review that lower body 1RM increased more when strength training was done first in the same session with endurance training. In contrast, order of training mode had no impact on changes in aerobic performance. One can easily reason that benefit of doing strength training first is that the quality of training is higher. If you are fatigued from endurance training during your strength exercises, you will lift less weight, which will stimulate less strength specific adaptations and subsequently lead to smaller increases in strength and muscle mass. Another possible reason lies on the molecular level.

Adaptations in opposite ends

Studies done with rodents and cell cultures have showed that signaling pathways activated by endurance training are found to inhibit acute anabolic response from strength training but not the other way around. Although, this effect hasn’t been reliably demonstrated in humans. (Fyfe et al 2014.) If we remove all the fancy words, this would mean that endurance training might block some processes in muscles which are important for increasing muscle mass and strength. Luckily, we have a way to work around this problem.

Signaling pathways activated by endurance training have been found to return to baseline levels after about 3 hours. Therefore, molecular interference shouldn’t be a problem if endurance training is performed at least 3 hours before strength training. On the contrary, anabolic response after strength training lasts at least 18 hours. (Baar 2014.) This leads us to the classic separation where endurance training is performed in the morning and strength training later in the day. With this order the molecular interference is smallest if both modes of training must be performed in the same day.

Optimize your recovery

Is 3 hours of recovery then enough between training sessions? Robineau et al. (2016) investigated how performing endurance exercise after different recovery periods (0h, 6h and 24h) after strength exercise affects strength and aerobic performance development. Strength increased less in 0h group compared to 6h and 24h groups. Aerobic performance increased in all groups but most in the 24h recovery group. Also, Sporer and Wenger (2003) concluded that total work that can be done during strength training is diminished for at least 8 hours after endurance training. Diminishing of work capacity seems to also be localized to the muscle groups used in preceding endurance training session. By these studies, separation between modes of training should be over 8 hours and in a most optimal situation at least 24 hours.

Pick your poison carefully

Wilson et al. (2012) found out in their review that cycling doesn’t affect as much interference in strength adaptations as running does. At least two reasons might explain the difference: running inflicts muscle damage due to its striking nature whereas cycling doesn’t, and cycling activates muscles in a similar pattern that typical strength measurements does. In the other hand, Sabag et al. (2018) noticed the opposite. High intensity cycling interfered more with strength adaptations than high intensity running did so nothing sure can be said about which one is “better”. What’s common with these two studies though is that they both show that the interference effect is at least somewhat body part specific. Lower body strength adaptations are interfered more than upper body after what is considered a more lower body endurance exercise (running and cycling). If you run in the morning, it might be more beneficial to do upper body strength in the evening. If you do squats and deadlifts in the evening, you might do ski erg training in the morning. This doesn’t apply so well if your sport is lower body specific and changing up the modality of training isn’t really a choice. For recreational athletes and in functional fitness changing the modality between upper and lower body might just be a good thing.

Take home message

Concurrent training has a lot of things to consider, although we didn’t even get to volume or intensity of training. With few simple guidelines you can benefit from both training modes. It sure is a compromise between the two but the interference effect can be kept to a minimum with smart programming.

Key points to remembers when programming your concurrent training program:

• Strength training should be done first if both training modes are performed in a same session.
• Perform endurance training in the morning and strength in the evening, if you train twice a day.
• Separate training modes with over 8 hours of recovery.
• If possible, train different body parts in endurance and strength sessions in the same day.

References:

Baar, K. 2014. Using molecular biology to maximize concurrent training. Sports medicine 44 (2), 117-125.

Fyfe, J. J., Bishop, D. J. & Stepto, N. K. 2014. Interference between concurrent resistance and endurance exercise: molecular bases and the role of individual training variables. Sports medicine 44 (6), 743-762.

Hickson, R. 1980. Interference of strength development by simultaneously training for strength and endurance. European journal of applied physiology and occupational physiology 45 (2-3), 255-263.

Murach, K. A. & Bagley, J. R. 2016. Skeletal muscle hypertrophy with concurrent exercise training: contrary evidence for an interference effect. Sports medicine 46 (8), 1029-1039.

Murlasits, Z., Kneffel, Z. & Thalib, L. 2018. The physiological effects of concurrent strength and endurance training sequence: A systematic review and meta-analysis. Journal of sports sciences 36 (11), 1212-1219.

Robineau, J., Babault, N., Piscione, J., Lacome, M. & Bigard, A. X. 2016. Specific training effects of concurrent aerobic and strength exercises depend on recovery duration. Journal of strength and conditioning research 30 (3), 672-683.

Sabag, A., Najafi, A., Michael, S. & Hackett, D. 2018. The compatibility of concurrent high intensity interval training and resistance training for muscular strength and hypertrophy: a systematic review and meta-analysis. Journal of Sports Sciences 36 (125), 1-12.

Sporer, B. C. & Wenger, H. A. 2003. Effects of aerobic exercise on strength performance following various periods of recovery. Journal of strength and conditioning research 17 (4), 638-644.

Wilson, J. B., Marin, P. J., Rhea, M. R., Wilson, S. M. C, Loenneke, J. P. & Anderson, J. C. 2012. Concurrent training: A meta-analysis examining interference of aerobic and resistance exercises. Journal of strength and conditioning research 26 (8), 2293-2307.