The key to 360-degree muscle: 90-degree eccentric isometrics . It might seem like we’re throwing a lot of geometry at you, but the concept behind time under tension (TUT) is simple, says Joel Seedman, PhD, owner of Advanced Human Performance : “Perform the lowering phase of a movement in a slow, controlled fashion, usually 3 to 5 seconds; pause in the stretched position, typically around 90 degrees; then perform the lifting phase in a powerful yet controlled fashion.” Believe us, a time-under-tension workout can humble even seasoned lifters…Eccentric isometrics are like the pressure cooker of training. “Rather than mindlessly performing slow-tempo reps, you’re using the increased time under tension as a means to fine-tune your body mechanics and alignment, which requires more mental engagement and focus,” Seedman adds. If you want to forge functional muscle mass and strength while simultaneously bulletproofing the joints and connective tissue, give this 10-move, full-body eccentric i