The problem isn't lack of energy. The problem is muscle and cardio exhaustion. You feel great, not tired, just your muscles stop working and you run out breath.

The problem isn't lack of energy. The problem is muscle and cardio exhaustion. You feel great, not tired, just your muscles stop working and you run out breath. So I don't think that vitamin, electrolytes, or more calories will help. If you're lifting seriously, you're already consuming plenty of those things.