In a world full of people slugging down caffeinated drinks all day, people who don't want or need caffeine can sometimes feel like second-class citizens. But in the gym, you can get many of the same benefits as people who take leaded pre-workouts. And as an added benefit, you won't find yourself shaking so hard the bar falls from your hands.

Research has shown that genetics play a significant role in caffeine sensitivity: Some people are highly affected by it, some aren't affected at all, and some are in between. Whether you are highly sensitive to caffeine, just don't like it, are trying to break a pre-workout-stimulant habit, or you work out late at night and don't want your sleep interrupted, non-stimulant pre-workouts offer a good alternative.

If you're looking for a single ingredient or two that could help your workouts, exercise physiologist Nick Coker labels these "The 4 Best Caffeine-Free Supplement Ingredients to Boost Your Workout."

• Citrulline malate: For increased blood flow and endurance
• Theacrine: For the same benefits of caffeine, without an energy crash or dependency issues (This ingredient is popularly known as Teacrine.)
• Alpha-GPC: A neurotransmitter prerequisite to help the nervous system maximize muscle activation
• Betaine: For longer-term size and strength gains

On the non-supplement end of things, a snack rich in carbs and protein 1-2 hours before a workout may be the best pre-workout you're not taking. Getting these calories and nutrients before a workout can give you long-lasting energy that'll power you even through long workouts. Avoid pre-workout snacks with a lot of fiber and fat, which take longer to digest and, for some people, can cause stomach upset during intense exercise.