Introduction: Testosterone is an anabolic steroid that plays key roles in growing muscles, enhancing physical performance and appearance, maintaining bone density, sex drive and sperm production. It is highly sought-after by athletes for its ability to accelerate muscle growth. Acute testosterone increase can be reached pharmacologically using testosterone replacement therapy (TRT) which is proven to have many harmful side effects including testicular shrinkage, prostate enlargement, and can lead to death. Physiological ways to increase testosterone such as resistance exercise have been shown to be an efficient way of significantly increasing testosterone without any harmful side effects. 

Objective: The aim of this systematic review was to show the impact of free weights and resistance training on acute testosterone levels and to assess the effects of physical activity on testosterone. 

Methods: PubMed was researched with the intent to include all articles which are written in English in all formats, peer reviewed, that study the effects of free weights and machines on testosterone in male adults.

Results: This study yielded 11 eligible studies. A total of two studies compared free weights in relation to testosterone. Three studies used resistance training intervention in the study program. Six articles used free weights resistance training intervention in the study program. The Effective Public Health Practice Project's (EPHPP) quality assessment tool for quantitative studies results rated two studies as strong, seven moderate and one as weak.

Conclusion: A more important increase in acute testosterone response was observed in individuals using free weights training compared to those using machine training. This is linked to the use of more muscles namely stabilizer muscles in free weight exercises. In addition to the type of resistance training, some important parameters should be taken into consideration. These include age, training volume threshold, training intensity, quality and quantity of sleep, short rest intervals and low adipose tissue percentage. Multiple gaps in knowledge were signaled in this review aiming to encourage further research regarding physical activity and testosterone.