We analyzed the available evidence and found that 39 studies or assertions support the idea that reaching muscular failure leads to similar muscle growth whether using light or heavy weights. No studies or assertions in our review contradicted this. What we’ve found so far suggests that the level of effort — specifically pushing a set until you can’t complete another repetition with good form — may matter more than how heavy the weight is. When people lift lighter weights to the point where their muscles are fully fatigued, the muscle-building response appears to be similar to lifting heavier weights to the same point of exhaustion. This doesn’t mean light weights are always better, or that heavy weights are unnecessary. It means that if you’re lifting light, you likely need to go all the way to failure to get a comparable result. If you’re lifting heavy, you might reach failure sooner, but the outcome in terms of muscle growth could be similar. This doesn’t apply to everyone. Some people may find it harder or riskier to train to failure with lighter weights, especially over long periods. Others may prefer heavier loads and find failure less necessary for progress. But based on what we’ve reviewed so far, the pattern points toward effort — not weight — being the key driver when comparing outcomes. The practical takeaway: If you’re using lighter weights, pushing to the point where you truly can’t do another rep may help you grow muscle just as much as lifting heavier. But if you’re already lifting heavy and stopping short of failure, you’re not necessarily missing out — just know that going to failure might bring you closer to the same result.