The influence of preworkout supplements on resistance training performance and subjective outcomes Original paper

Preworkout supplements consisting of multiple ingredients (e.g., citrulline, beta-alanine, taurine) have become increasingly popular in the sport supplement market. Although these ingredients have been associated with improvements in performance, much of the benefit derived from these supplements is often attributed to its caffeine content.

Noncaffeinated (sometimes referred to as “non-stim” or nonstimulating) preworkout supplements have gained favor with people who are sensitive to caffeine or who simply prefer not to have it in their preworkout supplement. These relatively newer preworkout supplements have raised questions regarding their effectiveness compared to their caffeinated counterparts.

This crossover study recruited 24 college-aged, resistance-trained participants (12 men and 12 women) who complete three training sessions and supplemented with (i) a caffeinated preworkout supplement, (ii) an identical noncaffeinated preworkout from the same manufacturer, and (iii) a placebo.

The resistance training outcomes used to measure the effectiveness of the supplements included squat isometric peak force, rate of force development, and isokinetic performance. Maximal strength was assessed for the upper body (bench press) and lower body (leg press) using the one-repetition maximum (1RM), and endurance was assessed using the same exercises while the participants performed as many repetitions as possible until failure or reps to failure (RTF).

Visual analog scales use a numbered scale on a continuum (e.g., 1–10 scale is very common) to subjectively rate the intensity of physical feelings or symptoms. In this study, visual analog scales were used to measure the participants’ perceptions of energy, fatigue, and focus, and scores were collected five times during each study visit (i) prior to supplementation, (ii) after supplementation and before isometric and isokinetic testing, (iii) after completing isometric and isokinetic squat testing and prior to bench press 1RM and RTF assessments, (iv) after bench press RTF but before leg press RTF, and (v) after the leg press RTF (which signified the completion of the study visit).

Neither the caffeinated nor the noncaffeinated preworkout supplement resulted in improvements in leg press or bench press strength and endurance. The only exception to this occurred during the leg press 1RM, where specifically males in the noncaffeinated group fared significantly compared to other groups.

Interestingly, however, the researchers did observe a slightly higher improvement in rates of force development in the noncaffeinated group versus the caffeinated group, with the former reaching statistical significance and the latter trending in that direction but didn’t quite reach that statistically significant mark. But this only occurred in the first 50 milliseconds of the rate of force development test, as supplementation did not affect the results between groups when rates of force development were tested up to 200 milliseconds.

However, both versions of the preworkout supplement resulted in improvements in maximal force production during an isometric squat test. The only significant effect of caffeine in this study was that the participants who took the caffeinated formulation of the preworkout supplement had higher subjective perceptions of energy, and this effect was likely to be expected.