Stewart Athletic Development


A beginners guide to Hybrid training part 1: Physiology and nutrition

To push the envelope on both resistance training and cardiovascular training, is known as concurrent or hybrid training. Examples would be people who engage in strength sports (Powerlifting, weightlifting & strongman) whilst also engage in endurance events such as distance running, cycling, rowing or triathalons.  Often, they will not only engage in the training for these events, but actively compete in both. These people are collectively known as hybrid athlete’s (and mad bastards), That being said, there are people who do it recreationally. Thus, this article series will be aimed at both competitive and non-competitive hybrid athlete’s (or those who are considering it)

The world of concurrent training is both niche and nuanced (and also super fascinating! Although maybe that’s just me..) with some layers of complexity to it that many other sports or training types don’t get. The aim of these articles (there will be 4 in total)  is to 1) help you understand concurrent training on a deeper level and 2) give some practical recommendations which you can apply to become a hybrid athlete from a training, nutrition and recovery perspective. These are big articles, so get a cup of tea or beer and strap in.

As an overview. Article 1 (this one) will cover the physiology underpinning cardiovascular training, strength / resistance training and how they interact with each other when it comes to hybrid training. There will also be some practical recommendations around nutrition and nutritional advice for hybrid athletes. Article 2 will cover some practical training recommendations around the aerobic & endurance training element of hybrid training. Article 3 will look at the resistance training and programming considerations for hybrid training and the final article will conclude with monitoring training and recovery methods & advice for concurrent training. But please remember, these articles are designed to compliment each other, and you will need each one to get a thorough understanding of concurrent training.

If you have ever spent any time in a gym, you may have heard a gym bro saying “cardio kills gains brah”. Looking around the gym, there are plenty of powerlifters / weightlifters who get out of breath tying their shoes, and anything above 5 reps is cardio. Conversely, you have the marathon runner who is a walking lung but built like the side of a fiver.

If you have ever spent any time in a gym, you may have heard a gym bro saying “cardio kills gains brah”. Looking around the gym, there are plenty of powerlifters / weightlifters who get out of breath tying their shoes, and anything above 5 reps is cardio. Conversely, you have the marathon runner who is a walking lung but built like the side of a fiver.

At a glance, you might be inclined to believe that cardio does indeed kill gains. Then you remember the existence of athletes like Rugby players and CrossFit athletes, reminding us that indicating you can get jacked and tanned whilst also still being incredibly fit.  

However, “cardio killing gains” has a modicum of truth to it…kinda. This is due to physiological phenomenon known as “the interference effect” (More on this later – it’s very nuanced) but as a very brief summary: The interference effect is when the body is placed under two different training stressors, causing a conflicting physiological adaptation. The phrase “you can’t ride 2 horses with 1 arse” kinda rings true. But, the biggest problem with the interference effect is not the physiology per say, more that people don’t understand concurrent training or how to minimise it’s effects. Essentially, people don’t know how to programme effectively for it. So I hear you asking “how do you programme for concurrent training?”. Patience padawans. We will get there. We all gon make it.

Before we get into the “how” we can achieve both. We need to understand what happens to our body from a physiological perspective when we focus on each style of training separately (i.e aerobic training & strength / hypertrophy training). With a better understanding of both training types individually, concurrent training as a concept will make more sense. We will kick things off by looking at aerobic training.

Aerobic or cardiovascular training

Aerobic exercise is done to improve your “fitness”. Aerobic training is often referred to as cardio or conditioning. Aerobic fitness can be measured in a number of ways, but 2 of the most popular within endurance & hybrid circles (and by popular, I mean reliable – no one enjoys doing them) is a VO2 max test and a 3-minute critical power test (this one is particularly rank). VO2 max is simply your maximum oxygen consumption during intense or maximal exercise, and is measured in ml / kg-1 / min-1. With VO2, the higher the number the more aerobically trained you are.

Critical power is slightly different, as it is measured on watts (power outputs) which can be normalised to bodyweight, or just outright outputs. A 3 critical power test is an all out effort for 3 minutes, typically on a bicycle ergometer against a fixed resistance. You are essentially getting 2 tests in 1 here. Firstly, you get a Wingate anaerobic test (WAnT – a 30s all out effort) followed by your critical power reading. Your critical power, is the watts outputted in the last 30s of a 3 minute critical power test. Seriously, this test is utterly vile.

The theory is that during the first 2 mins and 30s, you will have depleted pretty much all of your anaerobic substrates, so the outputs are reliant on aerobic metabolism. Thus, giving an indication of fitness. Whilst it doesn’t measure O2 (Oxygen – unless you are hooked up to a gas analyser during the test) it does give some data on aerobic fitness. However, whilst a useful test, many struggle to perform this test due to it’s grim nature. I know a fair few people whom have not managed to complete this test.

So these are 2 methods to measure aerobic fitness, however, there are many more tests for determining aerobic capacity, however that is likely to be a separate article in itself. Keeping things on topic…

What is the purpose in cardiovascular training? . To improve cardiovascular system and aerobic metabolism i.e aerobic pathways for energy during activity or performance. Aerobic capacity underpins all human activity to some extent. If it didn’t, we would die, as we kinda need O2 in our lives. How much O2? Well that entirely depends on what activities you do. The more aerobic your sport or activity (s), the more O2 you need. So adaptations occur in the body from aerobic training?

After prolonged aerobic training, the body undergoes various cardiovascular, neural and muscular adaptations. From a cardiovascular perspective, there is an increase in stroke volume (SV – blood ejected from the heart per beat). When this increase in SV occurs, there is a decrease in heart rate (HR) and resting heart rate (RHR). This occurs simply because of the increase in SV, more blood being pumped per heart contraction means more O2 transportation, therefore the heart doesn’t need to work as hard, so it slows down. This means that HR’s stay relatively lower at rest and during submaximal exercise. There is also an increase in maximal O2 uptake (VO2 Max), and over a prolonged period of time with consistent aerobic training, there is an increase in maximal cardiac output (Q). Q = SV x HR. This is a huge benefit from aerobic training from both a performance and health perspective.

From a neural perspective, the body becomes more efficient at moving, and improves exercise economy (You may have heard of running economy). Basically, the cost of movement from an energy demand is educed. From a muscular perspective, there is a delay in which the onset of blood lactate accumulation (OBLA) occurs, which is a huge factor in aerobic performance. In short, the longer you delay OBLA, the longer your body can use the lactate it produces as an energy source (I appreciate that Lactate is complex, I have done a video  on Lactate which can be found here – ). More information on lactate & hybrid training will appear in subsequent articles.

Aerobic training increases the size (Hypertrophy) of type I muscle fibres. These fibres produce less force (relative to type IIa and IIx) but are highly oxidative in nature and very resistant to fatigue, an advantage for aerobic training & endurance performance. There is also some conversion of type IIx (fibre type with most explosive contractile properties but very susceptible to fatigue) to type IIa, which produce less force than type IIx, but still considerably force more than type I. However, they are a little less susceptible to fatigue than type IIx (But more so than type I – I know, that is a little complicated).  Essentially, type IIa are kinda like the middle ground.

Aerobic training also increases mitochondrial density through mitochondrial biogenesis. I can hear you asking “What the fuck does that mean?” In summary, this increases the efficiency in which ATP (energy) is produced, thus benefitting performance. 

Keeping up? I know it’s a lot to take in, but it’s all important.

Finally, with cardiovascular training there is an increase in CaMKII (calmodulin-dependent protein kinase II) expression, and a downregulation in mTOR (mammalian target of rapamycin) expression. This is downregulation of mTOR is of particular importance, because mTOR (Alongside various other biological compounds) signal anabolic (muscle building) processes, including protein biosynthesis. Which we know, that protein metabolism is important for both growth and repair. Particularly, when trying to elicit strength, power and hypertrophy adaptations.

Keep all of this in mind and refer back to it if needs be.

Resistance training

Resistance training can be used to develop strength, power and muscular hypertrophy (Muscle gain) and is the key to getting jacked and tanned. I have covered how to achieve hypertrophy in a previous article ( ) which I would recommend checking out. I won’t go into too much detail on it here, but there are elements I will need to cover for concurrent training.

When we partake in resistance training, there are 2 main changes with occur: Neural adaptations and Structural adaptations. Both of which are important and have a combined impact on strength, power and hypertrophy, but will occur at different rates, which needs to be considered.

Neural adaptations

Neural changes are one of the first adaptations to resistance training. You may be familiar with “beginner gains” where people who are new to resistance training see a large increase in strength very early into lifting. These beginner gains can occur for months, even up to a year before things begin to slow down. We know these adaptations in the first couple of months are largely neural, because structural changes (i.e muscle hypertrophy) takes months to occur (discussed later) even in beginners. But what are neural adaptations?

When we perform any kind of movement, skeletal muscles are sent signals (Action potentials) from the brain via neuron pathways. When we begin lifting, a lot of the movements are very unfamiliar to us and feel difficult. When we practise these movements, they become easier over time. This is because the body becomes more efficient at sending these neural signals to the joints and muscles via neural pathways, which create movement. Over time they learn the pattern and become more efficient throughout the movement and is one of the reasons thinking “movements not muscles” is a far better way of viewing training. From a neural standpoint, there is also an increase in rate coding, which is simply the speed in which action potentials are sent from the brain to the muscles. This becomes very important for strength, max strength and especially important for power training.

Neural adaptations are not just seen in beginners. They can be seen in athlete’s of all levels of experience. However, the more trained the athlete the slower the rate of adaptation becomes, and the magnitude of gains are also decreased.  Athlete’s who are more experienced may (not always) need more frequent changes (but still structured) in exercise selection to ensure the stimulus is consistently high enough to elicit adaptation. Neural adaptations can also occur when utilising variations of certain exercises. This is something strength sport athlete’s are very good at achieving. Examples being powerlifters and weightlifters using non-competition exercises / modalities such as tempo’s, pauses, speciality bars, accommodating resistance etc. Westside barbells Conjugate training (and variations of) are further examples of manipulation of exercises / training styles to elicit neural adaptations (And also structural adaptations).

Structural adaptations

If resistance training is continued over a long period of time, the body will undergo structural changes as well as neural. These structural changes take far longer to develop, but what are these changes specifically? Firstly, we will look at skeletal muscle anatomy.

Structurally muscle fibres are (broadly speaking) divided into 2 types. These are 1) Parallel-fibred muscles, where the length of the fibres are close to the length of the whole muscle and 2) pennate muscles. These pennate muscles are short muscle fibres which are at an angle to the main muscle fibres and connective tissue. This angle is referred to as “pennation angle”. When we get stronger and more powerful, the incline of this pennation angle increases, allowing more force to be produced. Increased pennation angle is also correlated with greater hypertrophy. As we know, a bigger muscle has the potential capacity (but is not always the case – training is an important factor here) to produce more force than a smaller muscle, due to this pennation angle as well as having a greater cross-sectional area (CSA).


And of course, from resistance training, we also increase muscular CSA (I,e more lean muscle tissue). The extent to which it occurs will depend on several factors such as nutrition, training and whether it’s a desired adaptation (i.e are you trying to minimise or maximise hypertrophy). As mentioned, I have previously written about hypertrophy in greater detail, so I will not be going into too much detail here, but there are some points I do want to discuss.

Looking at muscle tissue, we know there are 3 types (as a reminder – type I, Type IIa & Type IIx). When we pack on lean muscle tissue, it is typically type IIa (and to a lesser extent type IIx – depending on the training type (discussed in article 2) muscle fibres which grow. Which is great, as you now theoretically can produce more force. However, muscle is a live tissue, and therefore requires O2. The larger the tissue, the greater the O2 requirement to supply blood flow and remove waste products. The hypertrophy of type IIa & IIx muscle fibres, alongside the increase in skeletal muscle tissue itself means that the muscles are more susceptible to fatigue, and will fatigue quicker. This is why someone like a bodybuilder will gas out very quickly on repeated sprint training (as well as not being conditioned for it).

Finally we will look the biochemistry of resistance training. When we lift, and also when we recover from nutritional intake (discussed below) there are biochemical and hormonal signals sent out for growth and repair. These signals cause an upregulation of anabolic compounds (Testosterone, human growth hormone, insulin, insulin-like growth factor-1) and mTOR (A kinase which plays an important role in muscle protein synthesis – which we know is important for building muscle tissue)all of which over time will lead to an increase in lean muscle tissue.

See the problem? aerobic training suppresses mTOR expression while increasing CaMKII & AMPK expression. Whereas resistance training increases mTOR expression. Essentially, a conflict of interest occurs. This is physiological effect is known as the “interference effect” and is where the statement “cardio kills gains” essentially comes from. A broken clock is right twice a day, and occasionally a gym bro will get something right (or at least be somewhat right). Although I would bet you a fiver they couldn’t explain why if you asked them…

Does this mean you can’t get jacked as well as getting fit as f*ck?. No, not at all. You absolutely can. You can absolutely improve your aerobic fitness and get jacked and juicy as well. And not just in a general sense, you can push yourself and boundaries on both training times, concurrently, if you wish. You just need to know how (More on this later). It is not uncommon. Hell if anything, concurrent training and being a hybrid athlete is gaining in popularity. People are bored of one dimensional training, and want to be better rounded from a physical perspective.

But there are some extra considerations and caveats which go into concurrent training. That being said, with some smart programming, training and recovery.. the interference effect is not a big a problem as you may think. But concurrent training is tough going. It is very demanding from a psychological and physical perspective, and will require effort and grit on your behalf.

So where do people go wrong with concurrent training?

As I previously mentioned, one of the biggest issues people face when designing concurrent training (arguably all training – but for the purposes here, concurrent training) is a lack of understanding. Specifically, lacking understanding of the physiology underpinning concurrent training, how to structure concurrent training, the energy and nutritional demands for concurrent training and also how to monitor training loads and recover properly from concurrent training. However, by the end of these 3 articles, you will hopefully have a better idea of what all these factors involve.

So, now that you have a better understanding of the physiology and the science behind concurrent training, we are gonna look at some practical recommendations from a nutritional and training / programming perspective. However, if you want to see just how far concurrent training can be pushed, I recommend checking out Alex Viada and the other coaches at – these guys are concurrent training guru’s and have achieved some ridiculous things). And even writing this article, my viewpoint’s on concurrent training and the interference effect have changed – So I would definitely recommend you check them out.

Nutritional advice for concurrent training

Nutritional overview

Unsurprisingly, concurrent training has a fairly high energy demand. This is especially true for the cardiovascular training portion of concurrent training. The greater the distance you cover in training, the more energy you need. That’s not to say nutrition for the resistance training portion is less important. Far from it. Both should be taken seriously.

The advice laid out in this article will be fairly simple, but easy to implement.  I will be covering nutrition for athletes in much more depth at a later date, but for this it will be nice and simple. If you are reading this and you are an endurance athlete (but not a concurrent athlete / undertaking resistance training) then a lot of this advice will still apply (also, start bloody lifting!)

When planning your nutrition, you need to have a clear idea of your goals in mind, from both a training and body composition perspective. However, body composition is likely to be less of a concern for concurrent athletes, unless your current composition is hindering performance (e.g carrying too much excess bodyweight). Simply, because your focus is going to be on fuelling performance and maximising recovery, and not your outward physical appearance.

As a broad nutritional overview, you are following the rules of calories in vs calories out (CICO) whether you realise or not. CICO is whats responsible for bodyweight, and inadvertently you will be doing 1 of the 3 things outlined below:

  1. Operating at maintenance calories – your calorie consumption is balanced with calorie expenditure (Both basal activity & exercise) Body weight will remain fairly constant (There will be daily fluctuations from salt, water and hormonal cycles if you’re female, but your average bodyweight will remain consistently )
  2. Operating in a calorie deficit – you are consuming less calories than maintenance, as a result you are losing bodyweight. Severity of deficit will dictate severity & rate of weight loss. Too severe a deficit / calorie restriction will inhibit performance
  3. Operating in a calorie surplus – You are consuming more calories than required to maintain current weight, therefore bodyweight increases. If trying to gain muscle mass, a small surplus is optimal. A large surplus will not increase the rate in which you gain muscle, but it will increase the rate in which adipose tissue (Fat mass) is gained. Too large a calorie surplus can inhibit performance.

The calories themselves will come from the 3 macronutrients which are discussed below, as well as some rough recommendations for nutritional intake

Protein – 4kcal per 1g of protein. Responsible for cellular function and muscle repair and growth. Will produce energy but is not efficient an energy substrate. Recommendations for endurance / concurrent athletes vary depending on the amount of resistance training undertaken, but can vary from 1.8 – 3.5g / kg of lean body mass (2.4g / kg seems to be optimal). If you are in a surplus, you can get away with the lower end of the recommendations (carbohydrates are protein sparing) and if you are in a deficit (not recommended -discussed below to why) you will need to be at the higher end of the scale to retain lean muscle mass. Ideally, spread between 3-5 meals per day, with 20-40g of protein per serving (20g minimum & 2.5mg + of leucine per serving). However, net protein over a prolonged period (e.g 72 hours) appears to be more important. So don’t sweat it if you miss a meal. As long as youre hitting your targets over a few days, you’ll be fine.

Carbohydrates – 4kcal per 1g of carbohydrates. Responsible for providing glucose for energy (through both aerobic and anaerobic metabolism) and also cerebral function. Carbohydrate requirements for athletes vary on the sport. For shorter, faster endurance events (such as 5-10ks etc) you may get away with 5-7g of carbohydrate / kg of bodyweight. For long / ultra distance athlete’s, it could be as high as 12g / kg of bodyweight.

Fats – 9kcal per 1g of fat. Responsible for providing energy through aerobic metabolism and also hormonal production / function and various other processes. For endurance / hybrid athletes intake, no less than 20% of total calories should come from fat (Although this p[retty much applies to anyone). The amount of kcal from fat will be dictated by your overall calorie needs, and also how much kcal are derived from protein and carbohydrates. Personally, I have found 22-27% of total kcal from fat to be fairly successful.

Nutrition in practise

You should be at minimum running around maintenance calories. How you operate at maintenance varies. Some people just like to consume the average maintenance. calories every day, not manipulating or undulating based on the training sessions in the week. Others may calorie cycle between surplus & deficit based on intensity & volume of their sessions. Essentially, they will eat more when training is higher in volume but lower intensity, and eat less when volume is lower but intensity is higher.

Cycling their calories in this manner will often put them at maintenance on average. If you are looking to either gain or lose weight, you can manipulate it as you see fit. It is worth remembering that when gaining weight, you want to at minimum maintain bw / kg outputs. No point gaining weight if you become slower (Applicable to explosive speed i.e sprinting and distance speed as well). However, if you are considering a deficit overall, I would take time to strongly consider why. Because concurrent training in a deficit is going to be infinitely more difficult.

Calorie cycling like this predominantly down to personal preference opposed to some super magic performance benefit. The logic is that you will need more fuel & recovery for the higher volume work, than the intensity work, which makes sense. As an overview, intake wise, you will require: 1) adequate protein to repair muscle tissue 2) adequate carbohydrate intake for energy and to allow recovery of glycogen stores & 3) enough fat for energy & also for hormonal & basal functions in which fat is required. This might seem simplistic, but in the case for the vast majority of cases in concurrent training (and all Strength and Conditioning) it is about mastering the basics.

However, a small surplus may be more beneficial, particularly if hypertrophy is a desired adaptation. By eating in a small surplus (typically 250-500kcal) you are putting yourself in a much better position to put on muscle tissue. Particularly, if you are stimulating muscle protein synthesis (MPS) at multiple times throughout the day. Building muscle isn’t just about calories, but sending the right signals (i.e triggering MPS and other anabolic signals / pathways) enough times to stimulate growth. The other advantage of being in a calorie surplus, is that you can consume more carbohydrates. Carbs actually have a protein sparing effect, so you can actually get away with eating slightly less protein whilst in a surplus, and still gain muscle. The key part here, is slightly.

Overall, by eating in a small surplus (Accounting for the energy expended via training- particularly through long distance endurance training) you are putting yourself in a better chance of building muscle. At the very least, you should be eating at maintenance. This is especially true for long and ultra-distance event athlete’s. If your focus is on shorter endurance events such as 5-10ks or half marathons (and similarly equated distances on bike, rowers etc) you will have a little more wiggle room and could get away with maintenance, or even a small deficit. But, that deficit is going to suck, and you will need to take a closer look at tracking and monitoring training loads and recovery (discussed in coming articles.)

To conclude, nutrition is a huge part in concurrent training for both performance and recovery. Thus, it should be taken seriously if you are looking to become a hybrid athlete. In the next article we will be looking at some practical aerobic training applications, as well as a closer look at the lactate threshold and lactate training, so be sure to check back!

If you have any questions about concurrent training, then shoot me a message! Or if you want to become a hybrid athlete, get in touch and we can discuss some hybrid athlete coaching!

Until next time

Stay strong