By Derek Hutson, American Council on Exercise Certified Personal Trainer
Many people do cardiovascular and strength training combined in the same session, also known as concurrent training. This method is primarily used because it allows the individual to complete multiple training objectives in a single workout. However, if your goal is to increase your maximal strength, then new studies show that concurrent training could be preventing you from reaching optimal strength gains. There are a couple of mechanisms within the body that work against each other during simultaneous strength and cardio-endurance training. The most notable are changes in muscle contractility, increased risk of delayed onset muscle soreness, and substrate depletion.
Muscle contractility is the ability of the muscles to contract when presented with a stimulus, and moderate-high endurance training has been shown to decrease contractility relative to increased strength (Docherty & Sporer 2000). However, other studies have shown that if running is replaced with cycling for endurance training, then the decrease in strength will be marginally less if not completely absent. This may indicate that cycling following resistance training is a better cardio option for those looking for maximal strength gains.
Delayed onset muscle soreness (DOMS) has happened to us all, and is the result of increased damage to skeletal muscle tissues that occurs after moderate-high load resistance training. One recent study showed that the presence of DOMS decreased strength gains over time in novice exercisers (Beck, DeFreitas, & Stock 2011). DOMS has been shown to be more likely and severe following a workout where a concurrent training method was used.
Whenever you exercise, there are 3 primary substrates (energy sources) that your body will use for fuel. The first and most commonly used during concurrent training and moderate-high intensity training is carbohydrates. The second is fat, which is utilized primarily during low-intensity exercise. The final energy source is protein, which is rarely used as it is so important for rebuilding muscle fibers. Cardio endurance training utilizes a great deal of your carbohydrate and fat stores during your workout. If cardiovascular training is performed together with strength training, there will not be as much carbohydrate and fat stores available after your workout to help your muscles recover properly.
Despite the drawbacks of concurrent training on strength, it is widely used for those with general fitness goals because it is one of the most effective methods of training for losing fat mass (Wilson et al. 2012). To remain healthy we all need at least 150 minutes a week of moderate intensity exercise, or 75 minutes of vigorous intensity exercise, paired with strength training 2-5x/week. Whether you pair your strength and cardio-endurance training, or perform them separate, the most important factor is that you are meeting these recommendations to stay strong and fit!
References:
Ashmore, Amy. Concurrent Training can Jepordize Strength Gains, Idea Fitness Journal. 12(4) P. 24-27
Beck, Defreitas, Stock, 2011, The Effects of a Resistance Training Program on Average Motor Unit Firing Rates. Clinical Kinesiology. 65 (1)
Docherty, D., & Sporer, B. (n.d.). A Proposed Model for Examining the Interference Phenomenon between Concurrent Aerobic and Strength Training. Sports Medicine, 385-394.
Wilson, J., Marin, P., Rhea, M., Wilson, S., Loenneke, J., & Anderson, J. (n.d.). Concurrent Training. Journal of Strength and Conditioning Research, 2293-2307.