If you are an endurance athlete, enthusiast, or just someone who wants to make sure you're getting the most out of your endurance sessions, you may be unsure of where best to fit strength training into your weekly routine. You may also even still be be doubtful about the benefits of strength training. Hopefully, in our previous articles, we have helped dispel some of the myths and concerns regarding this, and highlighted the potential for it to enhance economy and efficiency of movement in whatever endurance sport you partake in. Not to mention, all of its other benefits. However, whilst you are now hopefully aware of the ingredients, you still need to bake the cake. And in application is where it matters.
In practice, there are some things you need to think about when structuring your training week. You don't want strength training to interfere with your endurance sessions, as that is your priority. Strength training should supplement your training, not hamper your training.
So how does a strength training session potentially impair endurance performance, and what do we do to manage this appropriately?
There are numerous mechanisms which can explain how a strength training session can potentially impair an endurance session. For example, after performing a challenging resistance training session, we might get a reduction in the ability to contract muscle and thus a reduction in force production. This could be due to the accumulation of neuromuscular fatigue. Meaning, a reduction in neural drive from the motor cortex which impairs the activation of muscle. This reduction in muscle contractility could also be due to peripheral factors, such as reduction in muscle glycogen. Or it could be due to the exercise induced muscle damage specifically from the eccentric (lengthening) component of strength training. Or it could be... you get the drift; fatigue is complex - perhaps more on this at a later date!
What this means is when it comes to your endurance session, there is potentially a greater cost of work at a given intensity and/or a faster time to exhaustion. For example, being fatigued from a strength training session may impair economy. Economy being defined as the amount of oxygen needed to sustain movement at a given pace. Essentially, oxygen cost increases for the given work. This might be commonly seen in metrics such as an increased HR for a given intensity, or increased lactate levels, or increased rating of perceived exertion. This might be more problematic when your endurance sessions are intense, when the speed or wattage is at, or above, threshold due to the utilisation of fast twitch muscle fibres, and the need to recruit high threshold motor units. However, a question that needs to be considered here though; does all this really matter?
Well, it isn't necessarily a straightforward yes or no here, like most things, it's context dependent. There are many things that have to be considered. Hopefully the discussion below can help you make more appropriate training decisions based on your objectives;
I think first and foremost, as mentioned in the last blog post, we need to be cautious in interpreting some of the physiological markers of fatigue from exercise induced stress in general. Some bigger moving pieces need to be considered when it comes to understanding the magnitude of individual responses to training. Namely, the environment we lay training stress on top of matters most. Performing a lower body strength session on 3 hours sleep in the AM, under-fuelled and stressed out due to issues at work, and then 8 hours later going into a tempo running session is probably not very 'optimal', and that is little to do with the fatiguing 'consequences' of strength training. Put simply, the obvious impairments aren't caused from the inability to contract muscle due to a strength training session. Again, we get so focused on the optimisation of training variables, we miss the elephant in the room.
We also have to remember, training stress, if overlaid upon the appropriate environment e.g. adequate fuelling, good sleep, manageable life stressors, isn't a bad thing. In actuality it is good, very good. It's kinda the point. I think some people assume by adding something like two strength sessions into their training week they are suddenly going to jeopardise themselves. Again, the introduction of some strength training stress is the least of your concerns, for most people. Besides, just because your oxygen cost is maybe a little greater, your HR a little higher, and you're feeling a bit sluggish, perhaps due to the fact you did some strength training the evening prior to your endurance session, it doesn't really matter that much. Meaning, you will still get improvements. You will still see positive adaptations. The idea that the two cancel each other out, or the suggestion that everything in your training needs to be perfect for you to see progression and results, is untrue. It is also idealistic and a naive appreciation of the systemic nature of stress. If you're that concerned about doses of strength training, you may as well wrap yourself up in cotton wool.
Now, there are still better ways to do things of course. It all just sits on a scale of appropriateness, and we should try to stack the chips in our favour to get the most out of the primary objectives. So, it may not be the most appropriate to schedule an intense lower body strength session the day before you go into an intense running threshold session. And so we should look to separate our sessions so we can still keep the goal, the goal. Often a good rule of thumb is to leave 24-48 hours between those 'hot' sessions. However, the more accustomed you are to strength training, the less novelty of the stimulus, the less time you would need to recover. If the stimulus of strength training is novel for you i.e if it is something that is entirely new for you, then you should be more considerate of its impact. It also matters where localised fatigue occurs. There is very little concern from having an upper body strength session in the morning and then a tempo session on the bike in the evening, for example. Lastly, we should consider modality. We know that running requires a little more neuromuscular demand than 'off feet/non-impact' conditioning methods e.g. cycling, rowing and swimming. From my own experience I am far more cautious about making sure I give myself enough rest between my lower body strength sessions and running than I am about bike sessions.
When it comes to looking at the week in general, and from what we know about strength training more likely to impair more intense tempo and threshold sessions, then it perhaps might be more sensible to go into those sessions fresh, and plan your strength sessions closer to sub-maximal/steady state/zone 1&2 efforts. A good structure, and one for me that I currently use, is to focus on the more intense endurance (namely running) session at the start of the week, and my longer slower sessions towards the back end. I try to consolidate my lower body strength day with an easy bike, and then give myself a full recovery day afterwards. This I feel works best for me, where the sessions are divergent in intensity so they don't interfere with each other, but also mean I can enjoy the day off whilst still keeping my volume of bike training up where I would like it to be (competing in duathlon in September). This also works because typically I have Thursday afternoon out of the gym, and I have more time on weekends in general. Programmes are no more than artificial maps, and for them to be actionable they have to be realistically achieved! And when in doubt, just scale appropriately!
Be mindful, this is my weekly training, and in total, I have trained in some way shape or form for 20 years!
Ref: The effects of exercise-induced muscle damage on varying intensities of endurance running performance: A systematic review and meta-analysis. Dean Burt, 2023.
Compatibility of Concurrent Aerobic and Strength Training for Skeletal Muscle Size and Function: An Updated Systematic Review and Meta-Analysis. Moritz Schumann, 2022.
Training Considerations for Optimising Endurance Development: An Alternate Concurrent Training Perspective. Kenji Doma, 2019.
The progress theory podcast, Phil Price & Kenji Doma.
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