A training program that combines aspects of both strength and endurance training is commonly sought after by everyone from the top-level athlete to the casual fitness enthusiast.
While combining the two might sound simple enough, each type of training requires a different approach from an exercise standpoint and produces different biochemical responses within the body.
The potential benefits of combining both types of training seem obvious enough but are there also potential limitations? If so, what are some ways you can go about mitigating them?
Before we get into that, let’s first discuss some of the main differences between strength and endurance training. Making a clear distinction between resistance and aerobic exercise will help us to better understand how each type of training affects the body.
What is Strength Training?
We can think of different modes of exercise as existing on a continuum, with strength and endurance training existing on opposite ends of the spectrum.
Strength training, which is essential to sports such powerlifting and Olympic weightlifting, relies primarily on high-resistance exercises of short duration (as little as 1-3 reps per set) performed at or near-maximal intensity (usually at or above 70% of 1 rep max).
The ultimate goal of performing these types of exercises is to make our muscles as strong and powerful as possible.
Over time, when performed at the right intensity and frequency, high-intensity resistance exercise can increase strength and induce muscle growth.
The Science Behind Building Strength
So how does strength training affect the body’s biochemistry?
In simple terms, our muscles are an organized collection of cells containing different types of proteins, which each have a specific function within the body. Various modes of exercise target and engage different types of proteins.
Some proteins, which are commonly referred to as receptors, are specifically tasked with detecting stimuli. Once engaged, these proteins activate a unique network of signaling pathways within the muscle that allow the cells to respond and adapt to stimulation.
Strength training specifically stimulates myofibrillar proteins, which are responsible for producing contractions within the muscle.
Resistance exercise such as weightlifting can produce significant levels of stress on the muscle, which in turn can damage the tissue within it. The body responds to this type of stimulus by breaking down damaged parts of the muscle cell and replacing them with new tissue.
Ultimately, the muscle responds to stimuli such as weightlifting by rebuilding itself to better handle the demands of the exercise. Over time, this rebuilding process leads to increases in strength and size.
What is Endurance Training?
Looking at the other end of the spectrum, endurance training relies primarily on longer duration exercises, which can last anywhere from a couple of minutes for exercises of higher intensity to a couple of hours for lower intensity exercises.
In contrast to strength training, it involves low-resistance exercises such as running or cycling as opposed to weightlifting. The primary goal of performing these types of exercises is to increase the muscle’s capacity to perform low-resistance aerobic activity.
Over time, when performed at the right frequency, endurance training can improve your body’s overall oxygen uptake as well as your muscles’ capacity to maintain energy.
The Science Behind Endurance Training
How does endurance training affect the body’s biochemistry?
Unlike strength training, endurance training engages different receptors within the muscle. Aerobic exercise activates different networks of biochemical pathways that produce their own unique reactions and adaptions inside the muscle cells.
The specific type of proteins that are broken down and rebuilt by the body following endurance training — mitochondrial proteins — are responsible for regulating energy levels in the muscle cells.
Following endurance training, our muscles do not respond by getting bigger and stronger like with strength training. Instead, aerobic exercises such as cycling or running help us to increase the muscle’s capacity to stabilize energy levels within its cells.
The main takeaway here is that endurance training produces its own unique biochemical reactions within the body. The rebuilding process that takes place within the muscle following aerobic exercise does not lead to improvements in size and strength.
Should You Combine Strength and Endurance Training?
While some more specialized sports require training that is heavily geared towards one end of the spectrum, most sports require some combination of both strength and endurance training for optimal performance.
Even the casual fitness enthusiast is often interested in some type of training program that simultaneously builds strength and burns fat.
However, athletes and hobbyists who combine both resistance and aerobic exercise in their training often run into performance-related issues as they progress through their program.
In general, we can expect to see some improvements in our aerobic capacity over the course of a concurrent training program. Several studies have demonstrated improvements in performance indicators such as resting and working heart rate throughout a program featuring both resistance and aerobic exercise. Improvements in strength, however, may be more difficult to come by, especially in later stages of training.
For example, a study published in 2006 tracked the performance developments of a group of participants performing a concurrent strength and endurance training program over the course of 10 weeks. Each group member performed resistance exercises for 30 minutes per day, 5 days a week, and endurance exercises for 40 minutes per day, 6 days a week.
The researchers found that participants continued to show improvements in endurance-related performance over the entire course of the training program. Strength-related performance however only increased during the first 6-7 weeks of training, followed by a plateau and eventual decrease in strength by week 10.
The Science Behind the Interference Phenomenon
So why can endurance training impinge on our ability to gain strength in a concurrent training program?
As we mentioned earlier, each type of training activates different proteins and produces different reactions within the muscle cells. When resistance and aerobic exercise are performed in short succession of one another, the body is often unable to respond and adapt to both types of stimuli.
In such circumstances, the body tends to favor aerobic-based adaptions over strength based ones — the network of signaling pathways normally stimulated by strength training is overridden by the body’s biochemical response to aerobic stimulation.
Exercise scientists refer to this general finding as the “interference phenomenon”.
Researchers have found that the muscle’s ability to respond and adapt to strength training can become compromised in instances when over 20 minutes of aerobic exercise is also performed in the same training session more than 3 times per week.
A further study demonstrated that improvements in strength only became inhibited when both types of exercise engaged the same muscle group. For example, making strength gains can be much more difficult in instances when exercises such as cycling and leg pressing are performed within a short time frame of one another.
How to Minimize the Interference Phenomenon
So, we’ve seen that aerobic exercise can negatively impact our ability to develop strength and size in a concurrent training program, but is there anything we can do to get around this?
In order to optimize our muscles’ ability to respond and adapt to concurrent training, it is important to develop a clear understanding of what our training goals are. Doing so will allow us to structure our training program so that it ultimately produces results that align with our goals.
Prioritizing Your Training as an Endurance Athlete
The primary goal of endurance athletes such as cyclists, for example, is not surprisingly, aimed at increasing the muscle’s capacity to perform aerobically.
As a result, training programs in this area tend to be very endurance dominant. But what if you are a cyclist who also wants to build some muscle and strength over the course of your training program?
One way in which exercise scientists suggest you can do this is by focusing your endurance and strength training on different muscle groups.
As we discussed earlier, it is much more difficult for your muscles to get bigger and stronger in instances when they are tasked with adapting to both aerobic and resistance exercise simultaneously.
Consequently, if you are an endurance athlete primarily concerned with aerobic exercises that engage your lower body, targeting muscles in your upper body during your strength training will allow you to build more size and strength over the course of your training program.
Splitting up Training for Optimal Recovery
While the approach mentioned above may be beneficial for athletes in a sport where one particular muscle group is emphasized in training, it is less effective for athletes like swimmers, who often engage both the upper and lower body during aerobic training.
As we saw previously, when aerobic training is performed in short succession of resistance training that engages the same muscle group, the biochemistry induced by endurance training tends to win out.
Researchers have found that performing endurance and strength-related exercise on different days can reduce the likelihood of aerobic training interfering with your strength.
Allowing your muscles to react and adapt to each type of training at different times will help to reduce the amount of interference between aerobic and strength-related adaptations.
Doing your strength and endurance training on different days can not only be an effective means of minimizing strength loss, but it can also help to improve cardiovascular performance over the course of a concurrent training program.
A study published in 2015 demonstrated that improvements in cardiovascular performance over the course of a 24-week concurrent training program were greater in participants who performed strength and endurance exercises on alternate days.
Prioritizing Strength in Your Training
But what if your goal is to get stronger and leaner?
If your primary goal is to increase strength and burn body fat, incorporating High-Intensity Interval Training (HIIT) into your program can help to improve your endurance, burn fat and build strength all at the same time.
I recently spoke about this subject with Justin Roethlingshoefer, who is a strength and conditioning coach for the San Diego Gulls of the American Hockey League (AHL). He also works with the NHL’s Anaheim Ducks conducting fatigue and data management.
Not surprisingly, Justin is often tasked with developing programs that allow his athletes to make improvements in both strength and conditioning over the course of their training. One way in which he is able to do this is through the application of HIIT.
Instead of emphasizing lower-intensity, longer-duration aerobic exercises in his training programs, Justin is more focused on things such as sprints and agility based movements.
When asked what a typical training session looks like, he replied “We use a lot of interval sets, so like with our tri-sets (3 different exercises performed one after the other), it’s about 30-45 seconds worth of work, then you're getting some rest, then you're going back into it, it’s all timed.”
When combined with strength training, Justin has found that HIIT can be an incredibly effective means of building up fatigue resistance while simultaneously building strength and power.
The main takeaway here is that performing short intervals of high-intensity aerobic exercise will not only help you to improve your endurance and burn fat, but it will also help to assure that your body is able to react and adapt to strength-related stimuli during your training program.
As we saw earlier, a group of participants using a 10-week concurrent strength and endurance training program only saw diminished results in strength-related performance in the final 3-4 weeks of the program. This means that most participants had no issues with making progress in their strength training over the first 6-7 weeks.
Shortening the number of consecutive weeks that you perform high-intensity resistance training can help to reduce loses in strength over the course of a concurrent training program.
3-5 weeks of high-intensity resistance training followed by 1 or more weeks where the intensity is significantly reduced will better allow your muscles to react and adapt to strength training in a concurrent program.
If you are going to use a concurrent strength and endurance training program it is important that you know what your goals are.
Making simultaneous improvements in both strength and endurance depends on the successful management of multiple variables.
Prioritizing your training to reflect your goals is the best way to assure that your performance across both modes of exercise continues to improve throughout the course of your training program.