Strength and endurance based training
Two types of exercise training
Two of the most popular types of exercise training are strength training and endurance training. Depending on what your goal is, you may do more of one and less of the other, but most serious exercisers and athletes will be doing a bit of each. If, like me, you are a sprinter, the majority of your training will be power based – short sprints at high intensity, and heavy weight training.
However, there is still some place for endurance based training within this programme, perhaps prolonged bodyweight general circuits, or tempo-based running. Conversely, you might be a marathon or ultra-endurance runner. This will require you to spend a large amount of your training time running, often over long distances. The smarter ones of you will still be utilising weight training, just to a smaller extent.
Team sports such as soccer require a slightly more equal split – the modern footballer is required to possess explosive speed and jumping ability, be strong enough to survive the physical contact, but also have the endurance component to last the full match.
Understanding concurrent training
If you are undergoing both strength and endurance based training, then you are said to be taking part in concurrent training. Even the typical exerciser is probably doing this type of training, interspersing weight based resistance training with some form of cardio-vascular exercise. The problem with this type of training is that the adaptation pathways to resistance exercise and endurance exercise are very different. They even compete to an extent – endurance training appears to lower the strength adaptations from resistance training compared to individuals carrying out strength based training alone. This is known as the interference effect.
To understand this fully, we need to look at the mechanisms driving adaptation to exercise. As a simplified model, the adaptation to resistance exercise is driven by mechanical load upon cells, specifically muscle cells. This is augmented by growth factors and adequate nutrient availability. Because muscle hypertrophy is very costly from an energy point of view, at the cellular level there needs to be an abundance of energy available for hypertrophy to take place. If there is sufficient energy at the cellular level, then mTOR is released post-resistance training. mTOR is one of the prime drivers for muscular hypertrophy, and if it is blocked then hypertrophy doesn’t take place.
So far, so good. We know we need energy in the cell, and this will allow mTOR to be released. The problem then comes with the introduction of endurance training. Endurance training lowers the energy available within a cell substantially. This is good, from the endurance perspective, because the adaptations to endurance exercise are stimulated by metabolic challenges, which include a drop in ATP in the cell, as well as lower levels of oxygen, increased levels of lactate, and also increased amounts of reactive oxygen species (ROS). When the cell is metabolically challenged, it releases an enzyme called AMPK, which then increases expression of a number of genes associated with adaptation to endurance exercise. One of these is PPARGC1A, which increases mitochondrial biogenesis (creating more mitochondria), capillary density, and also substrate utilisation. All very important aspects of adaptation to endurance exercise.
However, we have a problem. If AMPK is elevated, from, say, an endurance training session, then this will prevent mTOR from being released. The two work in an almost antagonistic relationship, with high levels of one being determined by lower levels of the other. Just by taking a very surface look at this, we can see that it makes sense; AMPK is stimulated by low muscle glycogen, whereas mTOR requires high muscle glycogen for muscular hypertrophy to occur.
How to maximise concurrent training
So, what can we do to minimise the interference effect, and maximise the adaptations to both resistance and endurance training? The first is to not train both these areas in the same session; try to split endurance and resistance training into discrete training sessions. This could be two sessions within the same day, or resistance training one day, and endurance training the next. If you are following the two-sessions-per-day idea, then a big gap is probably better – ideally six hours. In a French study looking at amateur rugby players, strength gains from resistance training were lowest in those that did combined strength and endurance training in the same training session. This effect started to disappear with six hours between sessions, but the optimal was 24 hours (although this might not be optimal from a periodization or training load sense). Interestingly, improvements in VO2 max (a measure, but certainly not the only one, of endurance capacity) were also greater in those taking 24 hours between resistance and endurance sessions.
What should come first, endurance or strength training?
If you are going to train endurance and strength on the same day, then which should you do first? Well, it seems like it might be a good idea to start off with endurance based training. The reasons for this are two fold – if you do it earlier in the day, you could do it in a fasted state. This will further increase the metabolic demands on the cell, boosting endurance based adaptations to the exercise. AMPK is also “switched off” much quicker after exercise than mTOR, whilst mTOR needs slightly longer to exert its effect on muscular hypertrophy. Thus, if resistance training were to occur first, then mTOR would only be elevated for the six hours between sessions. If it happens later in the day, it can be elevated for up to 18 hours until the next endurance session.
Some other tips would be to try to increase the metabolic stress on the cell when undertaking endurance exercise – potentially doing it fasted (as previously discussed), or utilising high intensity training. After the endurance training session, aim to consume carbohydrate to increase muscle glycogen, setting the scene for optimal mTOR conditions later on. Essential amino acids (EAA) also help to stimulate mTOR, and so EAA consumption around resistance training should also improve the adaptive process.
Hopefully I’ve provided you with a very brief overview of some of the pitfalls of concurrent training, and a way to maximise your adaptations to both resistance and endurance based exercise.