How to juggle clients, recreational athletes, or athletes that have multiple goals? Many of them want to develop their muscular qualities (hypertrophy, strength, or power) at the same time as their cardiovascular endurance, but the development of the first limits the latter. It’s like saying too much is not enough.

This physiological phenomenon is called the interference effect, also known as competition, and refers to the case where endurance training limits the gains of a workout. This blog will discuss the mechanisms at play and how to avoid or limit the effects of retroactive interferences.

Here is a bit of science to start with:

To provide an adequate overview of the phenomenon, we studied a meta-analysis of 21 scientific articles (Wilson et al., 2011). All of the articles selected included three groups: a cardiovascular endurance training group, a strength training group, and a concurrent group combining the two types of training.

All participants completed a battery of tests before and after a training cycle, depending on their training conditions. The variables measured during the tests were hypertrophy, strength, and muscle power. In addition, maximum oxygen consumption (VO2max) and fat mass were measured.

First of all, the concurrent group had lower muscle gains compared to the strength training group alone. The effect size was not significantly different for gains in hypertrophy and strength but was significantly smaller for muscle power. Thus, muscle power is the variable most affected by interference.

This can be problematic for many athletes, where performance is based on muscle power and cardiovascular endurance (rugby, basketball, field hockey, etc.). For VO2max gains, the improvement in the concurrent group was similar to the one observed in the endurance group. These results show that retroactive interference is unidirectional and mainly affects muscle gains without altering cardiovascular gains.

Without going into detail about the physiology of exercise, two theories can explain the interference phenomenon. Firstly, the addition of cardiovascular training significantly increases training volume and decreases the recovery essential for adaptation. Considering these factors, participants expose themselves to overtraining that limits muscle gains.

Secondly, at the molecular level, one of the enzymes released during aerobic activity (activated adenosine monophosphate or APMK) inhibits a protein complex (mTORC1) which is responsible for muscle hypertrophy. Thus, aerobic exercise for more than 20 minutes at more than 60% of VO2max is sufficient to block the signals responsible for muscle development (Sabag et al., 2018; Wilson et al., 2011).

How to limit the effect of retroactive interference?

As mentioned above, team sport athletes are more likely to be limited by interference, as power and cardiovascular capacity are critical to performance. In addition, during periods of transition between seasons, these athletes do a great deal of physical preparation, increasing the likelihood of interference between workouts.

In addition to athletes, many gym clients or recreational athletes want to gain muscle mass while losing fat at the same time. We often offer them a combination of the two workouts, but again, the interference will interfere with the gains in muscle gain. In order to optimize the service to your clients, whatever their training level, here are some tips that you can easily put into practice to limit retroactive interference.

• Arrangement of sessions and recovery

Considering the metabolic cascade explained above, it is recommended that strength training be done after cardiovascular training to prevent oxidative signals from inhibiting protein synthesis signals at the muscle structure level. For example, for basketball players, technical training (throws, dribbling, finishing, etc.) may be done after strength training.

If this workout is the least cardiovascular, the gains made in strength training are limited. Therefore, it would be better to do weight training. In addition, it is recommended to have at least 6 hours of recovery time between sessions to ensure that there is no inhibition of protein synthesis. To really optimize the adaptation of both the oxidative and neuromuscular systems, it is recommended to have 24 hours of recovery time between sessions (Robineau et al., 2016).

• Cardiovascular training modality counts

Cardiovascular training done on the run would further limit gains in hypertrophy and muscle strength compared to the same workout done on a bike. One of the hypotheses put forward by the researchers is that running creates more muscle damage due to the sequence of concentric and eccentric contraction cycles. In contrast, cycling is mostly concentric (Wilson et al., 2011).

• The interference effect is specific to the region being trained

The effect of retroactive interferences is a peripheral and non-systemic phenomenon. Thus, a muscular solicitation of the upper body will not be affected by cardiovascular activity involving the lower limbs. As a trainer, it becomes easier to plan sessions by combining upper-body workouts with endurance sessions if sequencing is necessary (Wilson et al., 2011).

What to remember

An interaction between muscular and cardiovascular training limits gains in hypertrophy, strength, and especially power if both sessions are done without sufficient rest time between them. With the constraint of time in physical development in certain disciplines (or the need for certain clients to have quick results), the phenomenon of interference slows down the process.

The arrangement of training sessions over the course of a day with adequate recovery between sessions, their planning during a mesocycle, and the right choice of cardiovascular training modality are tips to manage retroactive interference better and optimize adaptation. It is important to note that interference is unidirectional and that strength training will not affect cardiovascular gains.