[1] Pre-workout supplements contain a variety of ingredients such as caffeine and creatine, differing by capsule or powder products.
[4] Between the late 1990s and early 2000s, consumers alleged that an active ingredient in Ultimate Orange, called Ephedra, caused high blood pressure, strokes, seizures, cardiac arrhythmia, and heart attacks.
[8] In the early 2000s, supplement companies created more potent forms of pre-workout that caused the blood flow in muscles to increase temporarily, giving lifters a better “pump.
[9] The product Jack3d gained notoriety for its potency, but its high concentrations of DMAA were suspected of causing shortness of breath, chest pain, and an elevated risk of heart attacks.
There is considerable overlap between the ingredients used in pre-workout blends and other supplements intended for weight loss, improving mood, life extension, or as purported nootropics or aphrodisiacs, although certain ingredients tend to be found only in products intended to assist in bodybuilding or athletic training.
Also, protein powders used to prepare the blend may sometimes be contaminated with melamine, a plastic precursor which is sometimes added to produce false positive results for nitrogen content.
[69][70] An increase in muscle endurance is primarily attributed to the large amounts of caffeine in pre-workout supplements.
[71][72][73] The ingested caffeine acts as an adenosine receptor antagonist, which serves to reduce overall pain experienced by the consumer and allowing them to work for longer periods of time.
The improvement in muscle recovery is associated with the branched chain amino acids (BCAAs) found in pre-workout,[75] particularly, glutamine.
[78] Caffeine also increases calcium release which allows for stronger muscle contractions during high intensity workouts.
[79] Studies also show that the caffeine in pre-workout improves focus and alertness in athletes as observed through a decrease in reaction-time in different settings.
Another issue that may arise is a higher risk in cardiac and liver related diseases due to the high concentration of caffeine in these types of products.