What research supports about effective training.
The single most important training principle: your body adapts to the demands placed on it. Increase demand progressively — more weight, more reps, more sets, less rest — and your body adapts. Without progressive overload, no training programme can produce continued improvement.
You get good at what you practise. Specificity says train for the adaptations you want. Variation prevents accommodation and works around the inevitable plateaus. The tension between these two principles is the core design challenge of any training programme.
Training provides the stimulus. Recovery provides the adaptation. Insufficient recovery means insufficient adaptation regardless of training quality. Sleep 7-9 hours. Manage stress. Take deload weeks every 4-8 weeks. These are not optional extras.