Following orders: make concurrent training work for you

The effect of endurance (E), strength (S) or concurrent training (S+E) on squat weight lifted. The endurance-training-only group was tested initially and following the 10-week training program. The strength-training-only group improved their squat performance by 40%, while the strength-plus-endurance group showed only a 25% improvement in squat performance. The endurance-only group as expected showed no significant gains since they carried out no strength training.

Understanding the concurrent training effect

To understand how the concurrent training effect arises, we need to appreciate that there are two key enzymes that play an important role in the effect of training on muscle. The first is ‘AMP-activated protein kinase’ (AMPK for short) and the second is the ‘mammalian target of rapamycin complex 1’ (abbreviated mTORC1) – see this SPB article for an in-depth explanation. Without delving too deeply into the complexities, AMPK stimulates endurance adaptations in muscle fibers and is activated by endurance exercise, especially when that endurance exercise is intense⁽²⁾. mTORC1 on the other hand is a signalling molecule, which is stimulated by intense resistance training and which is very highly correlated to improvements in muscle size and strength (see figure 2)⁽³⁾. Importantly, the maximal activation mTORC1 is between 30 minutes and six hours after training, but can be maintained for a full 24 hours after a single bout of resistance exercise⁽⁴⁾. suggesting that it is important to have mTORC1 active for a long time for it to maximally influence muscle strength.

Figure 2: mTORC1 and strength gains

The key thing to appreciate is that although these two different enzymes/signalling molecules are responsible for different aspects of training adaptation, they have the capacity to interfere with each other. In particular, when AMPK is activated following endurance training, it can block the activation of mTORC1, thus blunting the effect of any strength training carried out in the preceding hours. What this essentially means is that our innate biochemical makeup is restrained from improving both endurance and our muscle mass and strength at the same time – something that will come as no surprise to most experienced coaches and athletes! It also means that when the training is on the same day or within the same session, strength training should be carried out after endurance training and not vice-versa

What about the effects of strength training on endurance? Does the release of mTORC1 interfere with the activity of AMPK from a prior session? The answer seems to be no, which further strengthens (no pun intended!) the case for endurance training before resistance training. However, there is another type of interference that can occur even in an endurance first/strength second program. That’s because prior endurance training likely interferes with and suppresses the ‘neural drive; needed to create intensity during a strength session⁽⁵⁾. As we have discussed in previous articles, it is training intensity that provides the main stimulus for muscle growth and strength gains.

Concurrent training nuances

Athletes whose sports require strength and endurance excellence can use the above findings to help draw some general conclusions about how to train for simultaneous strength and endurance. In a previous article for our predecessor publication Peak Performance⁽⁶⁾, molecular biologist and sport scientist Professor Keith Baar of the University of California Davies summarized these training guidelines as follows:

·        Perform endurance training first and strength last.

·        Add intensity to your endurance (to maximise activation of AMPK).

·        Take food with your weights (to help switch off any residual AMPK and maximize the benefits of mTORC1 release.

·        Keep your strength sessions short (to develop maximize intensity).

·        Use negative repetitions (to maximize intensity while minimizing energy expenditure).

Subsequent observations from studies since then have largely confirmed these recommendations, but some nuances have become evident. In a meta-analysis study (a study that pools and combines all the data from previous studies on a topic to come up with very robust evidence) published last year by a team of Dutch scientists, researchers investigated how the sex of an athlete affects adaptations in strength, power, muscle hypertrophy, and maximal oxygen consumption when performing concurrent strength and endurance training⁽⁷⁾. It also investigated how these concurrent training adaptations are influenced by an athlete’s strength and endurance training status (ie whether they are highly trained, moderately trained or relatively untrained).

When the data was analyzed, the ‘endurance before strength’ recommendation was generally validated but there were two key findings that were somewhat unexpected:

·        Compared to strength-only training, concurrent training (ie adding in endurance work) resulted in blunted lower-body strength adaptations in males. However, this effect was NOT observed in females. In other words, it may be less important or even unnecessary for female athletes to follow the ‘endurance before strength’ recommendation.

·        When it came to training status, untrained individuals displayed impaired improvements for maximal oxygen consumption with concurrent training. In other words, compared to endurance-only training, adding in strength work as part of a concurrent program resulted in less endurance gains. However, this result was NOT seen in trained and highly trained athletes.

Put simply, the notion that strength training doesn’t interfere with endurance adaptations might be incorrect for novice or recreational athletes, implying that it may be better for these athletes to build up a decent aerobic fitness base by endurance-only training for a few months before considering adding in some strength work.

Concurrent training and weight management

So far, we’ve discussed concurrent training in the context of athletes whose sports require excellent levels of both endurance and strength. However, there is another dimension to concurrent training, which is its use for improving body composition and as a weight management tool. Over the past decade or so, evidence has emerged that when the goal is to improve health, all-round fitness and body composition (ie a reduction in body fat and gains in lean body mass), a combined program of both endurance and resistance training is superior to either alone⁽⁸⁾.

This approach is also recommended in the current World Health Organization (WHO) guidelines, which also emphasize the importance of regular engagement in both endurance and resistance training. Moreover, recent research on overweight populations has concluded that concurrent training programs are superior for improving metabolic health compared to either endurance or resistance training alone^(9,10). However, when weight management and body composition is the priority, what is the best training order in a program? Is it endurance first, strength second as recommended above? Until recently, this has not been properly investigated, but now a new study has provided clear answers.

New research

In this study, which is was published last month in the Journal of Exercise Science and Fitness, a team of scientists from the University of Beijing, China investigated how different sequences of concurrent training performed over 12 weeks impacted physical activity, body composition, and physical fitness in young overweight males⁽¹¹⁾.  Forty-five men, with an average age of 22.4 years and a BMI of 29.8 (moderate overweight), were enrolled in the study. To qualify for the trial, all the men had to be otherwise healthy, had conducted no regular or concurrent physical training within the preceding six months and were able to maintain a relatively consistent lifestyle and dietary patterns throughout the trial.

Before the intervention started and again at the end of the 12-week training program, all the men underwent assessments for strength (using isometric and isokinetic leg strength tests), aerobic capacity (VO2max – using shuttle run testing) and body composition. The body composition testing was conducted via an advanced technique known as Dual X-Ray Absorptiometry (DEXA), which is a highly accurate method of determining total body fat, body fat distribution, lean body mass, muscle mass and bone density.

What they did

Following initial testing, the participants were randomly assigned into one of three training groups (15 participants per group):

·        Concurrent CRE – resistance training followed by endurance training.

·        Concurrent CER – endurance training followed by resistance training.

·        Control group – controls who underwent no intervention and maintained their regular daily activities.

The training sessions for the concurrent groups were held three times a week and each 60-minute training session was structured into three distinct components: a warm-up, concurrent training, and stretching. Strength training encompassed a repertoire of exercises comprising bench press, deadlift, deep squat, shoulder abduction, abdominal work calf raises, and bicep curls. Throughout the training sessions, increasing intensity levels (ranging from 50% to 80% of 1-RM) were employed alongside a reduction in repetitions for all exercises, except for abdominal and plantar flexion exercises.

The endurance training sessions were standardized to last for 30 minutes and training intensity was incrementally elevated from 55% of maximal heart rate during the initial week to 75% max heart rate during the final week of the intervention. Throughout the 12-week intervention, all the participants wore a special actigraph sports watch, which constantly monitored and recorded their physical activity. In addition, the participants were instructed to keep a meticulous 3-day food diary on three occasions: at the beginning of the intervention, during the intervention and also at the end of the intervention in order to analyze calorie and nutrient intakes for the three groups.

What they found

The first (and unsurprising) finding was that compared to the control group who did no training, both the CRE (resistance followed by endurance)and CER (endurance followed by resistance) groups demonstrated significant enhancements in daily physical activity, body composition, and critical physical fitness metrics, including muscle strength and cardiorespiratory fitness. However, when comparing the results between CRE and CER, it became apparent that the CRE group (resistance followed by endurance) had made remarkable progress in terms of total fat loss and declines in body fat % and improvements in various other indices, such as maximum strength, explosive strength, and muscular endurance – improvement that surpassed those achieved in the CER (endurance followed by resistance) group (see figure 3).

Figure 3: Changes in various indices with different concurrent training structures

Mid grey bars = control group; light bars = CRE (resistance followed by endurance); dark bars = CER (endurance followed by resistance). Graphs from top left: weight, BMI (body mass index), total fat mass, BF (total body fat %), total fat-free (lean) body mass and android fat (the accumulation of fat mainly around the trunk and upper body type of fat, and which is associated with a higher risk of developing certain diseases, such as type 2 diabetes and cardiovascular disease.)

Practical implications for athletes

Gathering together the findings presented above, we can make some further recommendations about how to structure concurrent training. For athletes in regular training, when developing maximum strength and endurance is the goal, the evidence is heavily in favour of performing endurance training first then moving onto resistance training. Using this order allows the activity of growth/strength promoting mTORC1 to be maximized, without interfering with the activation of AMPK. More generally, athletes should try to refrain from performing their next bout of endurance training for 24 hours after their previous resistance workout.

However, something of a caveat is required here. If an endurance session consists of very high-intensity training, getting the best from resistance training those muscles immediately after endurance training will be difficult due to the accumulation of muscle fatigue from the endurance session. So for example, if you are performing sprint intervals on the bike or running track and are planning to perform squats when moving to resistance exercises, you will struggle! If you can, try and leave some time for recovery in between, or use a less intense endurance structure. Also, novice athletes may be better to build an endurance-only base forst before progressing onto concurrent training.

When it comes to concurrent training and improving body composition/weight management, the study discussed above⁽¹¹⁾ suggests that the usual endurance first, resistance second rule does NOT apply. Indeed, the reverse seems to be true – ie resistance training before your endurance training will likely produce better reductions in body fat, while simultaneously delivering good fitness gains. Yes, it’s true that this study was carried out on relatively untrained subjects so some caution is required. However, the basic human physiology of athletes and non athletes does not really differ greatly so there’s no reason to believe that this approach won’t apply to an athlete in training. Therefore a ‘resistance first, endurance second’ approach is definitely worth considering when fat/weight loss is the main goal. Examples include athletes who are returning to training after an injury and are needing to shed a few extra pounds, and early-season training following a holiday or rest in the off season when the pounds inevitably creep back on!

References

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8.       Concurrent Aerobic and Strength Training: Scientific Basics and Practical Applications. Schumann M., Rønnestad B.R Springer International Publishing; Cham: 2019. pp. 293–307

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11.     J Exerc Sci Fit. 2025 Feb 8;23(2):112–121