what is the best excercise routine for 40 year old male

For a 40-year-old man, a sensible starting routine is three resistance-training sessions per week, emphasizing safe, well-performed compound movements, plus one or two high-intensity interval sessions if recovery allows. Build up gradually, especially if you’re new to lifting. 1

• Compound lifts and technique: Prioritize multi-joint movements—such as squats, deadlifts, presses, rows, and chin-ups—but choose movements you can perform safely and with good form. 2 3
• Weekly sets: Aim for roughly six to ten working sets per muscle group per week as a practical maintenance target. The discussion notes that muscle size can decline about 1% per year after age 40 without resistance training. 4
• HIIT: Keep interval efforts brief and very hard, with recovery between bursts; one or two weekly sessions are suggested in the age-specific guidance. 5 6
• Training blocks: Vary training emphasis in blocks; one example is using 8–12 weeks of lower-repetition strength work before returning to higher-repetition training. 7

The best routine is one you can perform consistently and recover from; adjust exercise selection and workload to your experience and abilities. 8