We haven’t normally got much time for the teachings of Jim Bro. As he discovers a way to make the leg press into a biceps workout, we’d rather focus on functional moves, to build muscle that doesn’t just look good in a vest. Until, that is, vest season arrives. Then suddenly we see the benefit of skipping legs day – just this once.

But curls aren’t the only way to build big arms. The quickest route to a torso you won’t want to cover up lies in the oft-ignored muscles around Jim Bro’s faves. Take those curls – they hit your biceps brachii, the muscle that flexes when you point the way to the beach. But your arm is mostly triceps – the muscle on the other side. Target your tris and you’ll discover 60 per cent more muscle to fill your sleeves.

Ditto for your chest. Yes, you bench – probably too much. Which means two islands of muscle that look suspiciously moob-like when they’re covered up. Hit the muscles around your pecs instead and you fill in the gaps, to give more size all over, and a shape that can only mean strength.

The good news is that ignored muscles grow fast the second they’re in the spotlight. Your body responds to change, so it’s hard to squeeze more from areas you’ve worked for a long time, without radically overhauling your diet or logging twice as long in the gym. But hammer a muscle that’s never been stressed before and it responds quickly, forced to grow because it’s overloaded the second you put weight on it.

Even if the vest weather doesn’t last, the body beneath will. And it will still look good beneath a snug crew neck when winter comes.

The Workout

The workout is split into two days, the first aimed at your back, traps and biceps, the second your chest, shoulder and triceps.

Go as heavy as you can without sacrificing form – the more weight you move, the more results you’ll see. Perform each workout once a week, with a legs workout between them. Well, there’s only so far we’ll let Jim Bro steer your training.

Day 1: Back, Traps, Biceps

Wide-Grip Pull-Ups

4 x To Failure
Grab a pull-up bar with a wide, overhand grip. From a dead hang, squeeze your shoulder blades together and pull your chest up to the bar. Pause, then lower. Repeat until you fail.

Lat Pull-Downs

4 x 10 Reps
Sit in the lat pull-down machine and grab the bar with an overhand grip. Drive your elbows down to bring the bar beneath your chin, pause, then return until your arms are straight.

Rear Cable Fly

4 x 10 Reps
Stand facing a cable machine, a handle in each hand attached to the top pulley. Start with your arms crossed, then move your hands apart so you finish in a crucifix position. Squeeze your shoulder blades and don’t shrug. Slowly reverse the movement.

Shrugs

4 x 10 Reps
Stand with a heavy dumbbell in each hand, arms straight. Shrug your shoulders up towards your ears, so the weight lifts up. Hold, then slowly lower.

Hammer Curls

4 x 8 Reps
Stand with a dumbbell in each hand, palms facing your legs. Curl the weight up to your shoulder keeping your elbow still, so your palms face at the top of the movement. Squeeze your biceps then slowly lower.

Barbell Curls

4 x 10 Reps
Stand holding a barbell in both hands, so the bar rests against your thighs. Keep your elbows still and curl the bar up to your shoulders. Squeeze your biceps then slowly lower.

Day 2: Triceps, Chest, Shoulders

Dips

4 x To Failure
Hold yourself in a dip station, arms straight and knees bent so your shins are parallel to the floor. Lean forward slightly and bend your arms to lower your body, until your elbow is at 90 degrees. Then drive yourself back to the start position. Repeat until you fail.

Dumbbells Incline Press

4 x 8 Reps
Lie on a bench set to 30 degrees, with a dumbbell in each hand. Hold them over your chest, palms facing your feet, then drive the weight straight up. Pause at the top then slowly lower the weight.

Dumbbell Pullover

4 x 10 Reps
Set the bench to flat and grab a heavy dumbbell. Hold it over your chest with both hands. Take the weight back over your head until your feel a stretch in your chest, then lift it back to the start position.

EZ Bar Skull-Crushers

4 x 10 Reps
Grab an EZ bar – if you don’t have one, a barbell will work – and lie back on bench with the weight held over your chest, arms straight, palms facing your feet. Bend your elbow so lower the weight towards your face, pause at the bottom, then lift it back to straight by squeezing your triceps.

Military Press

4 x 8 Reps
Stand upright with your feet together and a barbell held across your chest, palms facing forwards. Keep your back straight as you drive the bar up over your head. Pause, then slowly lower.

Lateral Raises

4 x 12 Reps
Hold a pair of dumbbells by your sides. With your arms straight, lift them straight out so your arms are in a line across your body, parallel to the floor. Pause, then slowly lower and repeat.