Ever feel like the barbell is heavier in the morning? You're not just imagining it. Our bodies run on an internal clock, and for most people, peak strength and power don't arrive until the afternoon or evening. This can be frustrating for athletes and lifters who have to train early.
But what if you could flip a switch and perform just as well at 9 AM as you do at 6 PM? A brand new, randomized controlled trial from 2025 published in the European Journal of Applied Physiology suggests that a simple dose of caffeine might be that switch.
This study dug into how caffeine affects strength, power, and endurance, specifically looking at how it interacts with the time of day. The results are a game-changer for early-bird lifters.
The Study: Caffeine vs. The Clock
Researchers wanted to answer two main questions: Does caffeine boost performance, and can it overcome the morning performance slump?
To find out, they recruited 13 resistance-trained men and put them through a rigorous, triple-blind, placebo-controlled study—the gold standard for research. Here’s the setup:
- The Dose: Participants took either 3 mg of caffeine per kg of body weight or a placebo (maltodextrin) 60 minutes before training.
- The Timing: They completed four separate testing sessions: morning with caffeine, morning with placebo, evening with caffeine, and evening with placebo.
- The Lifts: The tests focused on the bench press and back squat, assessing:
- Strength & Power: Barbell velocity and power output at various loads (25%, 50%, 75%, and 90% of 1RM).
- Muscular Endurance: Reps to failure with 65% of 1RM.
By comparing performance across these four conditions, the scientists could isolate the effects of both caffeine and time of day.
Finding #1: Morning Weakness is Real, But Caffeine Fixes It
The study first confirmed what many of us feel anecdotally: performance dips in the morning. In the placebo group, lifters were significantly less powerful and slower on their light-load (25% 1RM) sets in the morning compared to the evening.
Specifically, in the bench press, mean velocity was 8% lower in the morning, and in the back squat, it was 9% lower. Mean power saw similar drops of 7-8%.
Here’s the exciting part: taking caffeine completely erased this morning slump.
When the lifters took 3 mg/kg of caffeine before their morning session, their velocity and power at 25% 1RM shot up, matching their evening performance. For example, in the morning bench press, caffeine boosted mean velocity by 11% and mean power by 10% compared to the placebo. This single intervention leveled the playing field, making morning training just as productive as evening training.
Finding #2: A Potent Boost for Squat Strength and Endurance
Caffeine’s benefits weren't limited to fixing the morning slump. It also provided a significant performance boost, especially in the back squat, regardless of the time of day.
- Heavy Strength & Power: In the back squat, caffeine increased mean velocity and power at heavy loads (75% and 90% of 1RM) during both morning and evening sessions.
- Muscular Endurance: During the reps-to-failure test (65% 1RM), caffeine improved mean velocity and power in the back squat in both morning and evening trials. For the bench press, this endurance benefit was only observed in the morning session.
This shows that caffeine is a reliable ergogenic aid for lower-body strength and endurance, helping you move heavier weights faster and grind out more quality reps.
The Surprising Reason It Works (It's Not Just Neural Drive)
Here’s where the study gets really interesting. We often assume caffeine works by jacking up the central nervous system, increasing alertness and allowing us to recruit more motor units. To test this, the researchers used electromyography (EMG) to measure the electrical activity in the prime movers (pecs, delts, quads, and glutes).
Surprisingly, they found no difference in muscle activation between the caffeine and placebo groups.
Even though the lifters were objectively stronger, faster, and more enduring after taking caffeine, their muscles weren't showing any more electrical activity. This suggests the performance boost wasn't coming from the brain sending stronger signals.
So, what's going on? The researchers propose that caffeine's magic is happening directly within the muscle itself—what are known as peripheral mechanisms. This could include:
- Improved calcium release from the sarcoplasmic reticulum (a key step in muscle contraction).
- Increased sodium-potassium pump activity.
- Other metabolic effects that make the muscle more efficient and fatigue-resistant.
This finding challenges the common narrative and suggests that caffeine does more than just make you feel alert; it fundamentally improves your muscles' ability to produce force.
Your Actionable Takeaways
This study provides clear, practical guidance for lifters and coaches:
- Train in the Morning? Use Caffeine. If you're an early riser, a low dose of caffeine (3 mg/kg) is a scientifically validated way to counteract the natural morning performance dip and ensure you're training at your full potential.
- Calculate Your Dose. For a 180 lb (approx. 82 kg) person, 3 mg/kg is about 245 mg of caffeine. For a 220 lb (100 kg) person, it's 300 mg. Check your pre-workout or coffee to get the dose right.
- Expect a Bigger Boost on Leg Day. The ergogenic effects on strength, power, and endurance were most consistent and pronounced in the back squat across all conditions.
- It’s Not Just in Your Head. The benefits of caffeine are real and measurable, likely stemming from improved muscle function, not just a feeling of increased energy or motivation.
In conclusion, this research confirms that a modest dose of caffeine is a powerful tool for enhancing resistance training performance. It's particularly valuable for eliminating the morning performance slump, allowing you to hit the gym hard whenever your schedule demands it.
Reference:
Montalvo-Alonso, J.J., del Val-Manzano, M., Cerezo-Telléz, E. et al. (2025). Acute caffeine intake improves muscular strength, power, and endurance performance, reversing the time-of-day effect regardless of muscle activation level in resistance-trained males: a randomized controlled trial. European Journal of Applied Physiology. https://pubmed.ncbi.nlm.nih.gov/40478455/