Need more endurance? We’re not talking about the muscle fatigue that sets in after a few sets of an exercise. We’re referring to the involuntary reduction in workout intensity and motivation that can set in after 45 minutes of heavy lifting, running, or competitive sports. While it may be tempting to turn to pre-workout stimulants, many of them are a double-edged sword: While some can reliably increase energy and performance, habitual use can lead to reliance and some—like 1,3-DMAA—can lead to high blood pressure . Here are a few safer and non-stimulatory alternatives for keeping up with longer (45 minutes or more) workouts.