If you follow any bodybuilding circles you may have heard the term time under tension at one time or another. If this term is new to you then it’s very simple to understand. Time under tension (TUT) refers to the amount of time your muscles are being activated during the concentric (the act of lifting) and eccentric (the motion of releasing) motions of an exercise. So if you’re doing a bicep curl, when your actually curling or lifting the dumbbell, this is the concentric motion. While letting the dumbbell back down is the eccentric motion. The stress your muscles endure during both motions determine the amount of muscle you can ultimately build. One study set out to prove that increasing the time the muscles are under stress (TUT), will directly influence the effectiveness of the workout.
The study titled “The effect of varying the time of concentric and eccentric muscle actions during resistance training on skeletal muscle adaptations in women” will be analyzed
The method they took
Twenty-nine women with current resistance training experience, defined as adhering to a program of multiple sets of various upper and lower body exercises performed with 8–12 repetitions to failure, 2–3 times per week for a minimum of 8 weeks prior to recruitment to the study, volunteered to participate in this study. The women were separated into two different groups. One that placed more TUT during eccentric motion and one that placed more TUT during concentric motion. Muscle samples were obtained before and after training using the needle biopsy technique. Various 1 Rep Max strength testing was employed to determine the amount of weight each participant could lift throughout the study. Finally, both groups were matched for the total time spent under muscular tension (TUT) defined as the time to complete the CON muscle action plus the time to complete the ECC action, along with a 1 s pause between actions. The CON group performed the CON action in 6 s and the ECC action in 2 s, while the ECC group performed the CON action in 2 s and the ECC action in 6 s.
The method explained
Ok so all of that was pretty damn complicated. To summarize what they did in a simpler fashion, they had two groups of women. Group CON took a total of 6s to perform the concentric motion and only 2s to perform to eccentric motion. The other group did the exact opposite. Since all the women were already experienced with resistance training, the results of the study should be more controlled since muscle adaptation is different between trained and untrained humans. They submitted all the women to the same resistance training programs, diets, and the same 1 rep max tests to determine how much they could lift at the beginning and the end of the study. They took muscle samples during the study so they can look at the muscle fiber under a microscope to determine the physiological change that was made and compare the two groups.
The results are pretty conclusive. The entire purpose of the study was to prove that either method of increasing TUT would result in skeletal muscle hypertrophy. The 1 rep max increased significantly across all groups but specifically the eccentric motion or ECC group as seen in the graph below.
While the 1 rep max increased significantly more for the eccentric group, muscle hypertrophy was significantly greater in the concentric group. The use of a slow concentric muscle action time during training resulted in significant hypertrophy of both types I and IIA fibers, which was similar to the findings of other investigations that have not manipulated TUT but have employed combined actions based on the same submaximal CON load. The eccentric group only saw an activation of type I fibers.
This study gives great indication that anyone training for hypertrophy (which should be everyone) should be placing an emphasis on concentric motion when performing any resistance exercises. The difference in the muscle fiber activation shows that the emphasis during the concentric phase puts much more strain on all the fibers across the muscle. Between increased hypertrophy in the concentric group, the increased strength seen the eccentric group, and the overall body fat reduction across both groups, it would be extremely beneficial for everyone to start increasing time under tension to at least 6 seconds to ensure maximal muscle growth is achieved.