Cardio or weights first? - How to structure your workout
With so many of us struggling to fit workouts in we'll often combine strength work with cardio when we get the chance, but could this mean you get less from your exercise? There is a notion called the interference effect which describes that when you combine weights and cardio you're limiting your ability to adapt to strength work.
The short answer is do cardio first then strength training to allow strength training adaptations to occur without being impeded by the cardio pathway.
Now for the science...
Got it from this diagram?! Me neither let me explain...
At a cellular level there are two pathways that are activated when you're doing cardio or endurance exercise. The cardio pathway activates the enzyme AMPK (activated protein kinaese) which switches off protein synthesis (muscle building) in times of energy strain i.e. cardio. Endurance training can create a catabolic effect (protein breakdown) and blunt the effect of anabolic hormones.
The muscle building mTOR (mammalian target of rapamycin) pathway is activated when you do strength training, promoting protein synthesis. It has been seen that AMPK can block the MTOR pathway if you do cardio before strength training whereas it doesn't occur the other way around.
A meta analysis by Wilson et al. (2012) looked at the research in this area across 21 studies. They confirmed there was a negative impact on strength training in particular power, when slow endurance running was done prior to weights. Interestingly running was seen to have a more pronounced effect than cycling. This was attributed to the higher eccentric component of running causing more muscle cell damage so when it came to performing strength work the muscles were less able to.
It has been seen on multiple occasions that strength training does not cause any change to VO2 max (a measure of fitness) and if anything has shown signs of improving it when combined with endurance training. So concurrent training has been seen to be a good way to go about your training you just need to do it in the right order.
Wilson et al., (2012) saw that compared to strength or endurance training alone, concurrent training was the best way to improve:
both endurance and strength
Using concurrent training to your advantage has been seen to be a very good way to promote fat loss and although it pains me to say it, if you are STILL concerned about your muscles getting too big (which you shouldn't be if you've read this!) then always combining your cardio and strength training will limit your ability to have bigger muscles.
Keep heavy weights sessions and high intensity cardio to separate days
Do cardio first to give your muscles more chance to adapt to strength work
Avoid long slow (over 30mins) cardio sessions on weights days
Refuel post exercise - this will enable your body to adapt properly rather than think it's in 'survival mode' post exercise
Bell GJ, Syrotuik D, Martin TP, Burnham R, and Quinney HA. Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans. Eur J Appl Physiol 81: 418-427, 2000.
Hickson, R. C. (1980). Interference of strength development by simultaneously training for strength and endurance. European Journal of Applied Physiology and Occupational Physiology Europ. J. Appl. Physiol., 45(2-3), 255-263.
Wilson, J. M., Marin, P. J., Rhea, M. R., Wilson, S. M., Loenneke, J. P., & Anderson, J. C. (2012). Concurrent training: A meta-analysis examining interference of aerobic and resistance exercises.Journal of Strength and Conditioning Research, 26(8), 2293-2307.