If I told you I could have you building more muscle in 40 seconds, you'd probably think I was full of crap. If I told you I could boost your endurance in 70 seconds, you'd wonder about my sanity. But here's the thing: You can achieve both by making one simple change: focusing on time under tension (TNT).
TNT refers to the total time a muscle is under resistance during a set. It's a method of determining the amount of work a muscle performs. For example, during the Bench Press, if it takes you two seconds to lower the weight and two seconds to raise it, your time under tension for one rep is four seconds. Performing 10 reps in this manner brings your TNT to 40 seconds. (See Double Tension Training: Taking Your Dumbbell Chest Exercises to the Next Level.)
Research shows that to build muscle, you should perform eight to 12 reps in a set, whereas to develop muscle endurance, you should do sets of 15 to 30 reps. In terms of TNT, it is generally understood that if your goal is to build muscle, the ideal TNT is 40 to 60 seconds. For more muscle endurance, keep your TNT between 70 and 100 seconds.
Obviously, this all depends on your speed during a specific exercise. For example, during the Squat, if it takes you two seconds to lower the weight but only one second to raise it, your TNT for a rep is three seconds, so a 10-rep set (30 seconds total) doesn't get you into the optimal TNT range for muscle building. To build more muscle, you have two choices: Slow down your rep so that it takes four seconds total, or boost your total reps per set to 14, which would give you a TNT of 42 seconds (three seconds per rep x 14 reps = 42 TNT).
One of my favorite exercises to build leg muscle endurance is the Split Squat. Keeping the TNT guidelines in mind, lower for 2 seconds and rise for 1 second. Performing 25-30 reps on each leg is the perfect number to increase your muscle endurance.
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