Thursday, March 27, 2014

Time Under Tension (TUT) - Random Numbers or Forgotten Determinant of Training Success? What Does Science Say?

"Go slow, grow fast" - does it really work this way?
I have to admit that I didn't have time to write "complete" article, so I will just work out an introduction and a bottom line to a never-finished draft that discusses an - in my humble opinion -  still unresolved question:  "Does the time under tension, which must not be confused with the simple number of reps let alone the set, matter when it comes to strength or muscle gains?"  As I said, based on my knowledge of the contemporary literature this is still an unresolved issue. Mostly, because slow (by necessity) means "light weight" and is hard / impossible to distinguish from the rep-number.

The methodological issues are probably also part of the reason that it would be an exaggeration to say that there are only "few" studies that investigate the influence of the time under tension (TUT) on hypertrophy or strength gains - but alas, I have collected the science-crumps for you. So here you go (for a preliminary list):
  • Figure 1: Myofibrillar fractional protein synthesis (%/h; Burd. 2012)
    Low load + slow movement = high TUT ➫ increased protein synthesis -- The 175% increase in muscle protein synthesis in response to leg extensions that were performed with a TUT of 6s in the concentric, and 6s in the eccentric phase of the movement Nicholas A. Burd et al. report in their a 2012 paper in the Journal of Physiology is one of the is one of the few very concrete results from studies that were designed to isolate the effect of the time under tension (Burd. 2012).

    In view of the pathetic load (30% of the 1RM) and the matched volume, the practical relevance of these figures is yet highly questionable. For me personally, it is thus more surprising that the difference between ...
    • doing 12, 7 and 6 reps @ 30% of the 1 rep max to failure for 198±10 s 119±9 and 90±7s, respectively (SLOW condition w/ TUT of 606), and 
    • performing the same number of reps with the same weight, this time obviously not to failure, within 25±2s, 14±1s, and 11±1s, respectively,
    ...was not even more pronounced than the +/- 49% difference (175% vs. 126%) Burd et al. observed in their eight young male subjects after performin three sets of unilateral leg extensions. 
  • Longer TUT, greater anaerobic energy expenditure - Inspite of the fact that it appears logical that longer times under tension would be associated with increases in energy expenditure, you as a SuppVersity reader know very well that not all things that exercise and nutrition science is not necessarily logical.

    In view of the overall scarcity of literature it is thus more than worth mentioning that Christopher B. Scott's 2012 study into the effects of time-under-tension and weight lifting cadence on aerobic, anaerobic, and recovery energy expenditures found that both, the anaerobic (=glyoclytic) energy expenditure and post energy oxygen consumption (EPOC) were significantly increased, when you train with a cadence of 4:1 or 1:4 and a corresponding TUT of 25s instead of 1.5:1 (TUT = 15s).
    Figure 2: Anaerobic energy expenditure, post exercise oxgen consumption and total energy expenditure (all in kJ) in the low TUT (1.5:1.5; 15s) vs. high TUT trials (Scott. 2012)
    It is thus only logical (you see, sometimes there is logic in exercise science ;-) that the total energy expenditure in the 25s TUT trials was ~30% higher than in the 15s TUT trial with its 1.5s up : 1.5 down cadence (see Figure 2).

    In view of the fact that the majority of us are hopefully not hitting the gym to "burn calories" (learn why that's simply dumb), these findings are interesting, but of similarly irrelevant as the previously cited increases in protein synthesis in the Burd study.
  • Concentric tension time is key to muscle growth -- I know that broscience dictates otherwise, but the evidence from a human study by Gillies, Putman & Bell suggests just that: It's the concentric portion of the exercise that stimulates skeletal muscle hypertrophy in response to leg presses, parallel squats, knee extensions and knee flexions in 28 healthy young women with previous strength training experience (Gillies. 2006).
    Figure 3: Fiber area (┬Ám²) of type I & II fibers before and after the 9-week training intervention (Gillies. 2006)
    As you can see in Figure 3, the baseline fibre size(s) of the subjects were yet so different that the participants that had been randomized to the group with an emphasis on the concentric phase (4:1 cadence) had an unfair growth advantage compared to the ladies in the eccentric emphasis group.

    In view of the fact that the eccentric emphasis group did also record greater strength gains, it appears unwarranted to change your training regimen from explosive / fast concentric vs. slow eccentric movements to the "concentric emphasis" pattern with its 4s : 1s cadence that was used in the study at hand. 
  • Heavy and fast or "slow" and long - it does not even matter -- In 2006 and thus 6 years before the previously discussed study by Burd et al., Michiya Tanimoto and Naokata Ishii, two scientists from the University of Tokio conducted a similar, yet more realistic study which compared
    • Figure 4: Cross-sectional area of the knee extensor before (open bars) and after (solid bars) LST, HN, and LN exercise training for 12 wk (Tanimoto. 2006)
      a low-intensity training regimen [ 50% of onerepetition maximum (1RM)] with slow movement and tonic force generation (3 s for eccentric and concentric actions, 1-s pause, and no relaxing phase; LST), to a
    • a high-intensity training regimen ( 80% 1RM) with normal speed (1 s for concentric and eccentric actions, 1 s for relaxing; HN), and 
    • a low-intensity with normal speed training regimen (same intensity as for LST and same speed as for HN; LN)
    and found what most of you will probably already have expected: As far as muscle growth there was no difference to be seen between the LST and the HN regimen after 12 weeks. The LN = low-intensity, normal speed training on the other hand sucked was a total waste of time and did not increase the size of the quadriceps muscle that had been hammered with three sets thrice a week at all.
Bottom line: As a seasoned SuppVersity reader you should not need me to tell you that the data does not allow for a conclusive decision if (a) time under tension matters at all, and if so, if it may (b) actually be the main determinant of muscle growth.

The green dots are satellite cells, muscle precursors as they are built with high volume leg training | more
I know at first that may sound hilarious, but if you think about the average bro in your gym who complains about "no gains", he will either be making tons of reps at a velocity that generates a momentum that reduces the TUT of an already fast 1-s rep to 0.1s, or he will tell you that only hitting it hard counts and his three reps on the bench press which are over in 6 seconds should actually make him grow.

To elucidate if (a) or (a) and (b) was right, we would yet need at least a dozen of well-designed studies, where - just as it was the case in the Burd study - the time under tension is the primary variable and reps, sets and weights only a means to modulate it. Until this data is available, it does probably not matter that I didn't have to dig up each and every article on that matter that exists... and if it did, I will just write another article ;-)
  • Burd, N. A., Andrews, R. J., West, D. W., Little, J. P., Cochran, A. J., Hector, A. J., ... & Phillips, S. M. (2012). Muscle time under tension during resistance exercise stimulates differential muscle protein sub‐fractional synthetic responses in men. The Journal of physiology, 590(2), 351-362. 
  • Gillies, E. M., Putman, C. T., & Bell, G. J. (2006). The effect of varying the time of concentric and eccentric muscle actions during resistance training on skeletal muscle adaptations in women. European journal of applied physiology, 97(4), 443-453.
  • Scott, C. B. (2012). The effect of time-under-tension and weight lifting cadence on aerobic, anaerobic, and recovery energy expenditures: 3 submaximal sets. Applied Physiology, Nutrition, and Metabolism, 37(2), 252-256. 
  • Tanimoto, M., & Ishii, N. (2006). Effects of low-intensity resistance exercise with slow movement and tonic force generation on muscular function in young men. Journal of Applied Physiology, 100(4), 1150-1157.