Concurrent Training – A General Explanation

Adaptations to training stimuli are a complex cascade of events when looked at from the hormonal/molecular level. Training adaptations are commonly generalized to the principle of specificity which states, the system will adapt to the specific stress that is imposed on it (i.e. lifting heavy weights will make you stronger). To dive slightly deeper, from a muscular system standpoint you can impose 3 different stresses: Endurance, Hypertrophy & Strength. From a cardiovascular standpoint, you can also impose 3 stresses: Aerobic, Glycolytic and PCr (PhosphoCreatine) (Baechle & Earle, 2008). So what happens when a session consists of more than just a single stressor as commonly occurs during most training sessions? Is the body able to adapt equally to all of them? This post will take a look at this idea through a generalized lense to explain the concept of concurrent training (training muscular and cardiovascular systems simultaneously) and why we do not simply train every system, every session, all year to achieve peak form. 

The main two stimuli that I will focus on are hypertrophic effects on the muscular system and aerobic effects on the cardiovascular system. Hypertrophy is defined as an increase in muscle size and is traditionally targeted through resistance training with rep ranges of 8-12. Aerobic training is defined as cardiovascular training that utilizes oxygen in its energy replenishing process. Aerobic training is generally long duration, low intensity work (Baechle & Earle, 2008). 

There are two major pathways, that are initiated by either of the above training stimuli. Hypertrophy training will stimulate the AKT/IGF-1 → mTOR pathway (will call ‘Hypertrophy Pathway’ for the rest of this post) and Aerobic training will stimulate the AMPK → PGC-1⍺ pathway (called ‘Aerobic Pathway’ for the rest of the post). These pathways have one common protein that links them, TSC2 (Tuberous Sclerosis Complex 2) (Coffey, 2006). 

During and post-Hypertrophy training sessions, the Hypertrophy Pathway will be stimulated and inhibit the release of that linking protein, TSC2. If an Aerobic stimulus is also applied, the Aerobic Pathway will be stimulated, which will release/activate TSC2 (linkage). So what is the result of this conflicting activation and deactivation of TSC2? TSC2 activation will inhibit the Hypertrophy Pathway and TSC2 deactivation will inhibit the Aerobic Pathway. This interaction decreases the impact of both the Aerobic and Hypertrophy Pathways and therefore, inhibits the training adaptations that will occur (Coffey, 2006). 

Therefore, the general fall back to, if you want to get stronger and fitter then you need to do a lot of cardio and lift a lot of weights as stated by the principle of specificity, is a gross oversimplification. Specific adaptations to training will not always occur to the same extent. This is not to say that cardiovascular and resistance training should never be performed during the same session. This example was used more to emphasize the idea that you can’t expect significant improvements if you are trying to improve every system simultaneously. Programming needs to include this critical evaluation of what is the most important system(s) to target during each phase, not how to get everything better immediately.  

 

References

Baechle, T.R. & Earle, R.W. (2008). Essentials of Strength Training and Conditioning (3rd. ed.). Windsor, ON: Human Kinetics.

Coffey, V.G. (2006). The Molecular Basis of Training Adaptations. (Doctoral Dissertation). Received from Google Scholar.