For every person who lifts weights these days, it seems there are two who have a podcast about it. There are more bodybuilding tips promising greater strength and muscle than ever before, and along with them a ton of confusion; one buffed-up Instagrammer says lifting heavy will get you swole, while a well-known fitness personality has claimed in recent years that two 30-minute workouts per week netted him 34 pounds of muscle in a month.

There are undoubtedly many ways to skin the fitness cat. And even the most credentialed trainers and researchers admit they don’t know everything about how muscle building works.

But for those looking to develop bigger biceps or blow up their chest, there are a few, scientifically validated rules you need to follow — regardless of what @BuffGuy27 posts on Twitter.

3 Factors Affecting Muscle Growth
Recent research has confirmed that there are three primary triggers for increasing lean mass (a.k.a. muscle).

Mechanical tension
Muscles don’t grow unless they need to overcome a resistance, and, to a point, the harder you need to contract them, the greater the “mechanical tension” and resulting growth stimulus will be. It’s the ‘use it or lose it’ principle. The most effective way to do that? Grab a weight (or resistance band) and have at it. Research suggests that mechanical tension disturbs the integrity of a muscle, triggering a series of changes that ultimately results in increases in not only size, but also contractile strength and power. In general, the heavier weight you can lift with good form, the more tension you produce, and the more you’ll grow.

Muscle damage
Traumatic-sounding, but true: muscle damage — or more specifically, the micro-trauma to muscle and connective tissue that’s a natural consequence of resistance training — touches off a regenerative process that can stimulate the production of new muscle cells. Research shows that eccentric movements (e.g., the lowering phase of a bicep curl), which require a muscle to lengthen under tension, produce greater micro-trauma than concentric movements (e.g., the lifting phase of a bicep curl), which require it to contract.

Metabolic stress
You know the deep burn you feel in your muscles after sprinting up several flights of stairs or pounding out 12 to 15 reps on your last set of heavy squats? That’s the result of metabolic stress, which is the accumulation of waste products from anaerobic energy production, and research shoes that it can be a powerful stimulus for adaptation (i.e., muscle growth). Want to maximize metabolic stress? Do moderate-duration, high-intensity activities that causes burning in the muscles; think 45 seconds of max-effort bodyweight squat-to-presses or lunge-to-curls, or 30 seconds of max-effort sprinting.>>>READ MORE