Did you know that using barbells for lower body exercises lets you lift a substantial amount of weight. "The issue with dumbbells for exercises like squats and lunges is that grip strength is a limiting factor," says Schoenfeld. Because your lower body is generally much stronger than your upper body, your grip strength tends to give way long before your legs do. But using a barbell eliminates that problem.

So why would you want to use more weight? When it comes to your backside, more weight yields greater results. "My experiments have found that barbell exercises elicit the highest possible glute activation," says Contreras. "Though it's also worth mentioning that my clients who saw the greatest improvements in glute shape did so by using many methods of resistance, including bands and body weight, with barbells being a primary component."

If barbell training is new to you, try these tips from Contreras and Schoenfeld to use the barbell safely and effectively.

1. Newbies: Nail the proper movement patterns by using a smaller, shorter training barbell (15 to 30 pounds, compared with standard 33 to 45 pound barbells) or a 20-pound Body Bar.

2. Test your strength: If you can perform 15 goblet squats with a 30-pound dumbbell or 15 deadlifts with a pair of 20-pound dumbbells, you are ready to graduate to a barbell.

3. When the bar is placed behind the head, it shouldn't rest on the back of the neck; place it slightly lower, above the top of your shoulder blades. (It will feel secure when in place.) The bar should also not rest uncomfortably on bone. Narrow your grip to engage your upper-back muscles and create a cushion for the bar.

4. Keep your gaze straight ahead during lower-body exercises. This helps prevent rounding of the spine.

5. Use the markings on the barbell to center your grip; equal portions of the bar on each side of the body ensures it doesn't tilt one way or the other.