The Interference Effect

This article is a guest post from Hidde Weersma.  You can follow him on Instagram here.

In some sense every sport needs a mix of strength and endurance. A marathon runner, for example, needs some amount of strength to prevent themselves from collapsing on the ground, but can also use more traditional strength exercises to target muscular weaknesses and decrease injury risk. At the same time, a 100m sprinter can benefit from endurance training. This can help to increase recovery within, and between, training sessions, thereby helping to increase the total number of high-quality training hours.

Even so, there are multiple sports where a more balanced mix of both strength and endurance play a crucial role for performance. Examples include rowing, rugby, short-distance cycling, short-distance swimming, short-distance running and of course HYROX. In case of a HYROX, you need strength to move the sleds on the much-feared carpet, or to push yourself up from the bottom of a lunges, for example. At the same time, you need the endurance to efficiently cover the 8km+ of running, recover between the functional stations and make it all the way to the finish.

Because of the nature of HYROX, athletes need to combine training for both strength and endurance.  This is called ‘concurrent training’.

The difficulty with concurrent training is that the physical adaptations of strength training and endurance training can interfere with each other. Strength training will, for example, cause hypertrophy and a transition in the muscles to more fast-twitch type II muscle fibers (which are stronger but less durable). On the other hand, endurance training will cause the muscles to remain smaller (so oxygen can be more easily transported), and a switch to more slow-twitch type I muscle fibers (which are less strong but more durable). When a mix of strength and endurance training blunts the training quality, or the subsequent adaptation process, it is called the ‘interference effect’.

This creates an interesting paradox. As (HYROX) athletes we need a mix of strength and endurance, but simultaneously, we partly disturb the desired physical adaptations by combining a training program consisting of both strength and endurance training.

In the remainder of this article, I will hand you some tips and tricks to minimize the interference effect during you training process. One disclaimer is that these tips can possibly give you the impression that training ‘HYROX-specific’ might not be a good idea. That’s not necessarily the case.  Every type of training can have its time and place. I believe these tips are most helpful during the preparation period when you try to maximize your separate qualities for strength and endurance, or around your ‘HYROX-specific’ training sessions.

The interference effect can manifest itself in two different ways:

1. The acute effect. Here, an earlier performed training session(s) has a negative effect on the performance of the subsequent training session. An example could be that you are not able to perform your usual weights and reps during a lower body strength session when you performed a hard running session earlier that day.

2. The chronic effect. Here the adaptation process of an earlier performed training session is negatively influenced by the subsequent training session. An example of this could be that the adaptation process after a lower body strength session (i.e. muscle growth etc.) is blunted by performing a running session a few hours after the strength session.

Acute Effect Theory

The effect of endurance training on strength performance

Usually, well-trained individuals can perform a high-quality strength session after 6-8 hours of rest from an endurance activity. However, this depends partly on the total duration, intensity and contraction type of the activity (i.e. running based activities are mainly eccentric contraction based activities, whereas cycling/rowing are more concentric based movements).

More rest may be necessary when the endurance activity is of a particularly long duration, high intensity or when it primarily consists of eccentric contractions. There is evidence that more rest may be needed when the strength session consists of high velocity power-based movements (like the clean or snatch) compared to low velocity maximal strength efforts.

The effect of strength training on endurance performance

Very heavy strength sessions can decrease the quality of muscle contractions for up to 96 hours. However, when you are not pushing yourself fully to the limit, well-trained individuals can perform a low-intensity endurance session after around 8 hours of rest. At least 24 hours are necessary to perform medium/high intensity endurance sessions.

Chronic Effect Theory

The adaptation process after a strength session seems to be negatively influenced when endurance activities are performed later that day. These negative influences are limited when: 1) the endurance activity is very short (<20min); 2) the activity is a low-intensity continuous effort; or 3) the activity is a low-intensity effort with very short intense sprints (<15sec).

Interestingly, endurance related adaptations are not negatively influenced when strength activities are performed shortly after or later that day.

Summary

When combining strength and endurance in the same training session:

• When first performing an endurance activity, and after that a strength session, avoid strength exercises with a focus on high velocity power movements.
• Consider performing strength exercises for muscles not highly involved with the endurance activity. For instance, upper-body strength work after a cycling session.
• When first performing a strength session and after that an endurance activity, keep the total duration short (<20min) and the intensity low. A few short high-intensity sprints can be executed. 

When performing a separate strength and endurance session on the same day:

• It is advised to perform the endurance session before the strength session. Ideally you keep at least 6-8 hours of rest between both sessions. When this is not possible, it is worth considering the possibility of performing strength work with the muscles which were not highly involved during the endurance session. 

Periodization over the year

• When the competition schedule allows for a solid preparation period it is a very interesting consideration to apply a ‘block-periodization’ model. With a block-periodization model you prioritize, during a training block, one specific physical quality while only maintaining the other. This creates the opportunity to fully maximize your strength and endurance while avoiding the interference as much as possible. After that you can try to combine these two maximized qualities and bring your HYROX performances to a new level!

Finally, and perhaps most importantly, we want to add that whilst the interference effect DOES exist, please don’t let it scare you or stop you doing the work in training.  This article is just for information, tips and guidelines.  Just because something isn’t ‘optimal’ that doesn’t mean its not worthwhile.  If you, for example, need to do an hours endurance training on the same day as you’ve done some strength work, it’s still likely to be a net benefit that you do the training! Leaving it out altogether, because you are worried about the interference effect, probably isn’t the best approach! 

References:

Methenitis, S. (2018). A brief review on concurrent training: from laboratory to the field. Sports, 6(4), 127.

Schumann, M., & Rønnestad, B. R. (2019). Concurrent aerobic and strength training. Springer: Berlin/Heidelberg, Germany.