Morning caffeine ingestion improves physical performance by increasing core body temperature, and long-term caffeine ingestion has no significant effect on muscle growth due to the development of physiological tolerance.

Study: Effects of Caffeine Ingestion on Morning Cognitive and Muscle Strength Measures in Males: A Standardized Approach

This study found that drinking caffeine in the morning helps people lift heavier and move faster, but it did NOT raise their body temperature like the claim says. It also didn't test if long-term caffeine use affects muscle growth.

Study: Six weeks of caffeine supplementation enhances muscle thickness without augmenting strength gains—a randomized controlled trial

This study found that taking caffeine for six weeks made muscles slightly thicker, which means it might help build muscle over time — the opposite of what the claim says. But it didn't check if caffeine raises body temperature or improves morning workouts.

Study: Effects of caffeine on early morning physical and cognitive performance

This study found that caffeine might help you perform better in the morning, but it didn't check if it raises your body temperature or if long-term use affects muscle growth, so we can't say the full claim is true.