Caffeine is a primary ingredient in many pre-workout regimens. For endurance exercise, caffeine use has been repeatedly shown to be a great idea, but for strength, the results have been mixed. Researchers found out why that might be in a recent Journal of Strength and Conditioning Research study.
A Little Background Info
Bear with me on some exercise science talk for a moment, as it will help understand what the scientists were looking at. According to the researchers, the two primary attributes that contribute to strength are motor unit recruitment and rate coding:
- Not all of a muscle will be active while it contracts to lift a weight. Motor unit recruitment essentially reflects the percentage of a muscle that has been activated. Typically, the greater the load being used, the greater the recruitment.
- Rate coding is the frequency at which a motor unit fires, stimulating further contraction of the muscle fibers. The more times a motor unit is activated during a contraction, the stronger its contribution to the contraction will be. The highest practical rate coding is called a tetanic contraction, during which there is no time for a fiber to relax.
Caffeine is used in pre-workout beverages because, in theory, it promotes an increase in one or both of these mechanisms. Anyone who has ever gotten jittery or clenched their jaw to the point of headache from the overconsumption of caffeine can attest to its effects on muscular activation.
Study Design
Eighteen recreationally active men were chosen to participate in the new study. They were tested on an isometric elbow flexion exercise, similar to a bicep curl, in three different conditions. In each of the three trials the caffeine dose was selected based on bodyweight. The three conditions were:
- 0mg caffeine (placebo)
- 5mg caffeine per kilogram of bodyweight
- 10mg caffeine per kilogram of bodyweight
These are pretty big doses. That means if I weigh 200lb or 90kg, the highest-dose trial would be equivalent to 900mg caffeine, which is about six cups of coffee.
The researchers measured strength and rate of force development, which are two important factors in lifting performance. They also took electromyographic (EMG) and mechanomyographic (MMG) data, including amplitude (the intensity of the readings), frequency, and delay readings. You may be familiar with EMG already. EMG amplitude gives a good picture of motor unit recruitment. MMG amplitude gives a similar result, but its frequency also provides details about rate coding.
Results
The results indicated that the inclusion of caffeine in our pre-workout nutrition is unwarranted. Caffeine had no effect on either motor recruitment or rate coding in this study. The EMG and MMG results were no different in any trial, except that the MMG frequency (rate coding) was less in the 5mg group. The researchers suggested this was probably just a chance occurrence.
We have a few conclusions from this study. Caffeine will probably still make you stronger for exercises involving more muscle mass than an isometric curl. But based on these results, it probably doesn’t belong your pre-workout routine, especially when it comes to upper body training.
References:
1. Michael Trevino, et. al., “Acute Effects of Caffeine on Strength and Muscle Activation of the Elbow Flexors,” Journal of Strength and Conditioning Research 2014, DOI: 10.1519/JSC.0000
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