In the ongoing debate of strength vs size, many lifters lean towards the belief that heavier weights automatically lead to bigger muscles. It’s easy to see why: the idea that increasing load equals muscle growth comes with the perk of setting new PBs.

But while lifting heavy is an integral part of building strength, relying solely on heavy, low-rep training could mean missing out on key growth opportunities. If you’re committed to building mass, it’s crucial to approach your training with a well thought out lifting strategy.

Exercise scientist Dr Mike Israetel has frequently shared his expertise on the topic of strength vs size. In a new YouTube video, he gives an in-depth, comprehensive breakdown of the differences between training for the two goals.

Israetel explains that defining size is fairly straightforward, ‘Size is just how big any given muscle is. It is directly measured by what’s called ‘cross-sectional area’. So if you take an MRI of your whole bicep at every millimetre slice, whatever the biggest part of your bicep is cross-sectionally, like if we take this area out, and measure it – that’s how big your muscles are.’

This is essentially how much space a muscle occupies when viewed from the side. To measure CSA accurately, advanced methods like MRIs are used to capture slices of the muscle to assess its width at various points. It’s the most reliable way to determine how big a muscle is.

‘It can be proxied on a total body level by basically your fat-free mass, which is all of the fat mass in your body, subtracted from the rest, and so what’s left is muscle, bone and all that other stuff,’ Israetel explains. The key takeaway is that muscle size can be tracked over time through changes in fat free mass or body fat percentage.

The exercises scientist explains that unlike muscle size, which is simply about muscle volume, strength is a skill: the ability to produce force. The most straightforward way to measure strength is through one rep max testing, which is the maximum weight you can lift for a single rep of a movement, such as a squat, deadlift, bench press, overhead press or even pull-up. ‘Good-technique one-rep max, the most weight you can lift just one time, a weight you cannot get even one and a half reps with – just 1 rep – that is the gold standard of strength.’

But it’s not just about raw power, it involves several other factors that contribute to your overall ability to generate force. Israetel explains there are four subcomponents of strength that go beyond just muscle size:

Size

The bigger your muscles, the more potential for strength, ‘The absolute biggest difference between two different people in strength, is going to be accounted for by one is just more jacked than the other,’ says Israetel. ‘You see a person with pecs that pop out phone book style, they probably don’t bench 40 kg – it’s probably more like 150.’ Just like a larger engine in a car can generate more power, more muscle mass gives you the potential for greater strength.

Muscle Architecture

How your muscles are aligned plays a role, according to Israetel. ‘If you train for a specific movement, let’s say the bench press, the actual alignment on a microscopic scale of your muscle fibres changes in your triceps, in your front delts and in your chest to align with a specific bar force pattern that you are training yourself to do,’ he explains. Strength training specific to a lift, like the bench press, leads to changes in muscle fibre orientation, improving efficiency in the movement.

Technique

‘In strength training you have to practice the technique that lifts the most weight for you,’ says Israetel – and that technique can depend on different factors. The way you perform a lift significantly impacts strength output. A proper technique can unlock more strength even without adding muscle. Strength athletes and Olympic weightlifters, for example, spend years refining their technique.

Neural Drive

‘You have to be able to switch on all of the biggest parts of your biggest muscles, maximum, and that’s neural drive,’ says Israetel. Neural drive is the mental and physiological ability to activate your muscles to their fullest potential. Practicing maximum intent during your lifts allows you to recruit more muscle fibres, therefore increasing strength. Your neural drive essentially taps into your brain’s ability to fire muscles with maximum force.

Israetel explains the key differences between strength and size as follows:

Muscle-Focused Techniques vs Movement-Focused Techniques

Israetel says a big difference between the two is in technique: muscle-focus technique versus movement-focus technique. ‘Let’s use the squat as an example, how does the technique look different? First is: bar position.’ The exercise scientist continues to explain that for most powerlifters or those who want to gain strength, the low bar position is best. For those who want to gain muscle size, the high bar position is best.

This is because overall:

• For size, focus is on maximising muscle tension on specific muscles, like the quads in a high bar squat, to stimulate muscle growth.
• For strength, the emphasis is on movement efficiency. So optimising the lift for maximum weight with the best movement economy, which often involves using multiple muscle groups and therefore prioritising the ability to lift heavier. For example, the low bar squat, which helps you ‘leverage you back better’, according to Israetel.

He also mentions other key technique differences such as squat depth. He explains that for strength training, we are usually choosing ‘the path of least resistance’ during the rep versus mind to muscle connection for size.

• Size involves a wide rep range, generally between 5 to 30 reps per set. This allows for a mix of lighter and heavier loads, aiming to fatigue the muscle to stimulate growth.
• Strength primarily focuses on 4 to 8 reps per set. The goal is to lift heavier weights with fewer reps, making it more about raw strength rather than muscle size.

To elaborate, Israetel says, ‘Really most of your strength training should occur with sets of 4 to 8 repetitions. Can you get stronger with sets of 9 and 10 as a beginner? Yes, but then everything works. As an intermediate? Definitely – but you would get stronger if you did sets of 4 to 8. Could you get stronger if you did sets of 2 and 3, even sets of 1? Yes, it’s just not the most time efficient or fatigue efficient way to get there.’

Relative Effort

‘How hard you’re trying in any given working set is very similar, but subtly different,’ says Israetel. He explains there are two big differences. One being that in strength training you work with rate of perceived exertion or reps in reserve (RPE or RIR).

He continues, ‘In most strength training, the technique work would be RPE 5: heavy enough to make you feel something but quite easy. And then most of your basic strength work working sets would be RPE 7, 8 and 9: tough, very tough but not all the way to the limit because going to failure is brutal on your fatigue, but not as big of a deal in hypertrophy training.’

Israetel explains that when training for size, you can train close to failure or to failure occasionally. To summarise, he says:

• For strength training: you do RPE and you go close to failure but not quite.
• For size training: you do RIR and you can get close to failure, not quite or you can regularly train to failure and get excellent results.

Volume

‘Strength training is going to require and be the most you can recover from, about two thirds of the volume of hypertrophy training,’ says Israetel.

‘When you are training for strength, you want to be able to have good workouts, but the progression is the big thing,’ He argues that if you’re not able to add weight each week, you won’t necessarily increase your strength in a meaningful way. ‘So what you want to do is train hard for strength training, but really hold back so that you can train hard again and heavy again next week.’

On the other hand, for size, he explains, ‘Fully exhausted muscles that just barely recover for their next session is probably the way to get the best gains. So if you’re really beat up from high volumes and hypertrophy training and muscle growth training: that just is what it is.’

Frequency

Israetel explains that the final difference is frequency. He says for hypetrophy training, all sessions for a muscle are hard. However, for strength, only one to two sessions per week are hard – the rest are 3 x 3s or 5 x 3s at 50% one-rep max or so, for technique maximisation and movement recovery for the next session.

Progression

‘For muscle growth training: [either] increasing in load or increasing in reps is rock solid, as long as you’re still in that 5 to 30 rep range,’ says Israetel, ‘Because you know you don’t want to increase reps to like 46 and you’re like “they said increasing reps is going to be good and I’m just getting the burn and I’m getting smaller” — don’t do that.’

To summarise, he explains: