WHAT HAPPENS WHEN YOU COMBINE STRENGTH AND ENDURANCE TRAINING?

Strength training and endurance training both have their benefits, but they have different mechanisms and effects.  We know strength training causes neurological and muscular adaptations beneficial for increasing strength and lean muscle mass.  Endurance training increases cardiovascular and metabolic efficiency.  Sometimes it is done for performance or leisure.  Other times it is used to burn excess calories to lose weight.  But what happens when you combine the two?  Do you still get the benefits of both or is one prioritized over the other?  This article will review the literature on the effects of concurrent strength and endurance training and the possible optimal applications.

Context is everything.  When we talk about strength training, it falls anywhere on the spectrum of resistance training to specifically increase muscle hypertrophy and strength.  We know strength training causes neuromuscular adaptations from motor recruitment to cross sectional area of a muscle fiber.  Endurance training can involve anything in a continuous elevated heart rate range.  Aka it is cardio.  We know the benefits to cardio, but we must be honest and point out that the main reason people do cardio is because they believe it is the best way for them to lose fat.  They are not entirely wrong, but at what cost.  And it is not my place to say what someone should do and should not do.  I am merely providing practical uses that are the most optimal.

Strength is the main issue when it comes to concurrent training.  The development appears to be inhibited with concurrent training than strength training alone (Leveritt, 1999).  Some studies even suggest that if the primary goal is strength, endurance training should have a low frequency while high volumes of endurance training inhibited lower-body strength (Jones, 2016). 

There are many mechanisms that could cause strength to be inhibited.  One of the possible causes is the neural effects on motor unit recruitment (Nadar, 2006). These neural implications could cause a limitation on rapid voluntary neural activation attenuating rate of force development, or explosive strength (Hakkinen, 2003).

This decline in neural activation is greater seen in Type II fibers after intense endurance training (Luginbuhl, 1984).  The change to myosin ATPase would suggest a change in population of these skeletal muscle fibers (Schantz, 1983).  What this suggests to athletes that are looking to be explosively strong and fast, avoid doing a lot of slow endurance training.

Another possible factor to the negative effects on strength is the effect of endurance training on muscle glycogen levels.  If you have read the previous articles, we talked greatly about muscle glycogen and how vital it is for energy.  Muscle glycogen levels decline after repeated endurance exercise and concurrent training (Costill, 1971).  These low levels of muscle glycogen could impair strength performance.

We obviously realize muscle glycogen levels decline after any strenuous exercise and adequate recovery helps replenish glycogen stores.  However, with the edition of endurance training, overtraining, in the sense of suboptimal glycogen replenishment, can affect optimal strength gains (Chromiak, 1990).  It has also been shown to reduce protein-synthesis rates (Dohm, 1985).  This effect on a key muscle hypertrophy component is shown in a study comparing low-volume concurrent training with low-volume strength training.  They found concurrent strength training blunted muscular adaptations compared to strength training alone (de Souza, 2014).  The cross-sectional area of Type II and Type I muscle fibers increased in the strength training group while the concurrent group saw no significant change in hypertrophy.  However, both groups found increases in muscular strength. 

Strength training can still provide benefits to endurance performance.  Master endurance athletes benefited from concurrent training due to improvements on running economy (Piacentini, 2013).  Strength training can increase rate of force development which would benefit any athlete in any physical activity.  Runners, cyclists, etc. must produce force to move.  The more force they produce the faster they move.  The more efficient they are at producing force, the less energy is required per stride.  It has even been suggested that endurance athletes could use a well-structured strength program to increase runny economy in preparation of events without effecting body composition (Piacentini, 2013).

There are obviously benefits from both training styles.  It all depends on your goals, and where you are currently at with your training.  Concurrent training can improve body composition, muscular strength, mobility, and balance if you have minimal training (Garcia-Pinillos, 2019).  It is important to keep in mind just because you see drastic results initially across the board does not mean that is how it will always be. 

We clearly found substantial evidence that concurrent strength and endurance training inhibits strength adaptations from neural activation, muscle glycogen, to protein-synthesis rates compared to strength training alone.  This is to be expected.  We also found evidence that strength training could greatly benefit endurance performance.

It is time to take all this evidence with a grain of salt to deduce practical applications.  Let us start with your goal.  If your goal is to improve your running or cycling performance because you compete in events or just because that is your primary goal, then strength training would be beneficial.  Adding 2 – 3 strength training sessions for a short period will improve running economy without inducing substantial hypertrophy.

If your goal is to get stronger, minimal endurance training.  If you must do endurance work, keep the frequency and volume low as in minimal times in a week and shorter distances.  High intensity would be best such as sprints, sled pushes, etc.  We talked about recovery and overtraining.  With concurrent training, proper recovery is vital or both aspects will suffer.

If your goal is to increase muscle mass, endurance training seems to impair muscular adaptations compared to strength training alone.  If you have very minimal training background, concurrent training could provide benefits initially.  But if your primary goal is to increase muscle hypertrophy, sticking with strength training will induce muscle growth more optimally.  That does not necessarily mean you cannot add muscle with concurrent training.  It means strength training is the most optimal way for muscle hypertrophy.

The other factor to consider is your training age.  If you were previously not training, any exercise is going to spawn results.  If you have been doing endurance training, but no strength training, the benefits of strength training will have great influence for your endurance performance.  If you have been doing strength training previously, chances are many neuromuscular adaptations have occurred to an extent and more training stimulus is needed to enhance growth.  Further endurance training could dampen additional strength improvements because of the possible factors previously discussed.

Again, I am not trying to say what you should do or not do.  I am providing practical uses based on evidence what is the most optimal mode of training based on your goals.  There is no absolute mode of training.

References:

Nader, Gustavo A. Concurrent Strength and Endurance Training: From Molecules to Man, Medicine & Science in Sports & Exercise: November 2006 - Volume 38 - Issue 11 - p 1965-1970

de Souza, Eduardo O.1; Tricoli, Valmor1; Aoki, Marcelo S.2; Roschel, Hamilton1,3; Brum, Patrícia C.4; Bacurau, Aline V.N.4; Silva-Batista, Carla1; Wilson, Jacob M.5; Neves, Manoel Jr3; Soares, Antonio G.6; Ugrinowitsch, Carlos1 Effects of Concurrent Strength and Endurance Training on Genes Related to Myostatin Signaling Pathway and Muscle Fiber Responses, Journal of Strength and Conditioning Research: November 2014 - Volume 28 - Issue 11 - p 3215-3223   

Cadore, Eduardo Lusa1; Izquierdo, Mikel2; Santos, Mariah Gonçalves dos; Martins, Jocelito Bijoldo1; Rodrigues Lhullier, Francisco L.1; Pinto, Ronei Silveira1; Silva, Rodrigo Ferrari1; Kruel, Luiz Fernando M.1 Hormonal Responses to Concurrent Strength and Endurance Training with Different Exercise Orders, Journal of Strength and Conditioning Research: December 2012 - Volume 26 - Issue 12 - p 3281-3288

Piacentini, Maria Francesca; De Ioannon, Giulia; Comotto, Stefania; Spedicato, Alessandro; Vernillo, Gianluca; La Torre, Antonio Concurrent Strength and Endurance Training Effects on Running Economy in Master Endurance Runners, Journal of Strength and Conditioning Research: August 2013 - Volume 27 - Issue 8 - p 2295-2303

Jones, Thomas W.; Howatson, Glyn; Russell, Mark; French, Duncan N. Performance and Endocrine Responses to Differing Ratios of Concurrent Strength and Endurance Training, Journal of Strength and Conditioning Research: March 2016 - Volume 30 - Issue 3 - p 693-702

García-Pinillos, Felipe; Laredo-Aguilera, José A.; Muñoz-Jiménez, Marcos; Latorre-Román, Pedro A. Effects of 12-Week Concurrent High-Intensity Interval Strength and Endurance Training Program on Physical Performance in Healthy Older People, Journal of Strength and Conditioning Research: May 2019 - Volume 33 - Issue 5 - p 1445-1452

Rønnestad BR, Mujika I. Optimizing strength training for running and cycling endurance performance: A review. Scand J Med Sci Sports. 2014 Aug;24(4):603-12. doi: 10.1111/sms.12104. Epub 2013 Aug 5. PMID: 23914932.

Dudley GA, Djamil R. Incompatibility of endurance- and strength-training modes of exercise. J Appl Physiol (1985). 1985 Nov;59(5):1446-51. doi: 10.1152/jappl.1985.59.5.1446. PMID: 4066574.

Leveritt M, Abernethy PJ, Barry BK, Logan PA. Concurrent strength and endurance training. A review. Sports Med. 1999 Dec;28(6):413-27. doi: 10.2165/00007256-199928060-00004. PMID: 10623984.

Hakkinen, K., M. Alen, W. J. Kraemer, et al. Neuromuscular adaptations during concurrent strength and endurance training versus strength training. Eur. J. Appl. Physiol. 89:42-52, 2003. 

Schantz, P., and J. Henriksson. Increases in myofibrillar ATPase intermediate human skeletal muscle fibers in response to endurance training. Muscle Nerve 6:553-556, 1983. 

Luginbuhl, A. J., G. A. Dudley, and R. S. Staron. Fiber type changes in rat skeletal muscle after intense interval training. Histochemistry 81:55-58, 1984.

Costill, D. L., R. Bowers, G. Branam, and K. Sparks. Muscle glycogen utilization during prolonged exercise on successive days. J. Appl. Physiol. 31:834-838, 1971. 

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

Dohm, G. L., G. J. Kasperek, E. B. Tapscott, and H. A. Barakat. Protein metabolism during endurance exercise. Fed. Proc. 44:348-352, 1985.