Neither repetition duration, nor number of muscle actions affect strength increases, body composition, muscle size or fasted blood glucose in trained males and females https://www.researchgate.net/public...ed_blood_glucose_in_trained_males_and_females Abstract A key variable within resistance training (RT) is that of repetition duration; the time (seconds; s) taken to perform the concentric and eccentric muscle actions of a repetition. Research has produced equivocal results with regards to strength and muscle mass increases whilst many studies have created parity in the number of repetitions though there has been a disparity in load used and time-under-load (TUL). The purpose of this study was to compare load, and TUL matched groups performing resistance exercise using differing repetition durations. Fifty-nine male and female participants were randomised in to 3 groups; 2s:4s (n=18), 10s:10s (n=20) and a group which performed a 30s eccentric, 30s concentric and 30s eccentric muscle actions (e.g. 1.5 repetitions; n=21). Participants were supervised in 1-on-1 RT sessions 2 d.wk-1 for 10 weeks. Outcomes were 10-repetition maximum (RM) and predicted 1RM for chest press, leg press and pull-down exercises, as well as body composition, upper arm and thigh muscle mass and fasted blood glucose. Analyses revealed significant increases in strength for all exercises but no between-group differences, and no statistically significant time course changes for the other variables. Repetition duration does not affect the increases in strength in trained participants where exercise is performed to momentary failure. Since time constraints and perceived difficulty are often cited barriers to exercise, it is important to recognise that the low-volume (single-set), machine-based protocol employed herein produced worthwhile strength increases in trained participants.
So basically what they are saying is that as long as you are going to failure the rep speed really doesn't make much difference.
I think the bottom line with training is that your body is going to adapt to whatever training style you put it through. So your best bet is to stay consistent with your training but periodically change your style just to keep your body from completely adapting.
I would have liked to have seen an equal fast set of moves such as 2s:2s. They did a 2s:4s and a 10s:10s as the shorter times. 4 seconds is still a slow recovery portion of most exercises. I doubt most people take 4 seconds to come up from a squat or bench press regularly, or even to lower arms from a bicep curl.
I really don't think it makes a difference as long as you're not using momentum to sling the weights either concentrically or eccentrically. And if there is a difference, I doubt it's meaningful to the point that you should do an exercise in a way that seems unnatural to you.
I just wonder why they chose those times since a control group to me would seem to be the normal up and down often done to contrast that with a mid and longer term movement. That would support the theory that time under load has no effect on blah blah blah. What it looks like to me is the study says if you want to put the muscle under durational stress, 4 seconds is as good as 30 seconds.
What is "normal?" Because I can tell you that a lot of the people I've seen, in every gym I've ever been a member of over the years, were using momentum to get the weights up and then just about letting the weights drop into beginning position before swinging the weights back up. That's poor exercise form, not really working the muscles to maximum effect because of the excess momentum involved, and unnecessary exposure to risk of injury. Why would anyone use this form for a control group? Why would anyone want to exercise in that manner, anyway?
http://baye.com/repetition-speed-recommendations/ ...This has been demonstrated with force gauge experiments and can be proven mathematically. I’ve discussed this with several friends who are engineers, one of whom shared the following: Assuming a typical range of motion of about half a meter, if you calculate the force required to bring a one hundred kilogram or two hundred and twenty pound barbell to rest over a distance of about four inches at the cadences listed below, you get the following percentage of the load used (gravitational constant rounded up to 10 and results rounded off to the nearest whole number): 1/1 cadence (.5 m/sec): 113% 2/2 cadence (.25 m/sec): 103% 4/4 cadence (.125 m/sec): 101% 10/10 cadence (.05 m/sec): 100% In other words, as long as the acceleration occurs over a distance of at least a few inches the difference in peak force between a 2/2 repetition and a 10/10 repetition is only a few pounds. If you double the distance over which acceleration occurs during the 1/1 cadence to eight inches, which is more realistic if you are attempting to reverse direction smoothly at that cadence, the percentage of load required to bring it to rest comes down to only 106%, which would neither be a dangerous level of peak force or significant variation in tension. The faster you go, the more difficult it is to reverse direction this smoothly, however. It becomes easier to turnaround smoothly as you go more slowly, but moving any more slowly than necessary to do so does not significantly reduce your risk of injury or improve the efficiency of muscular loading. With proper training and practice a three to four second cadence results in a slow enough speed on most exercises for most people to perform reasonably good turnarounds...
Lot of assumptions in your response that 1-2 seconds involves using momentum and poor form. I can do dumbbell curls under control with a nice weight and it does not take me 4 seconds to bring it down under control. Standing straight with elbows glued to my sides it is 1-2 seconds up and 1-2 seconds down under control. That is not improper form. It starts to get longer when my arms start to fail. Bench press is 1-2 seconds up and maybe 1-3 seconds down before up again. On straightforward back squats I don't see anyone doing a really long lowering of even more than 4 seconds (that is a really long time if you count it out loud). If the study was asking does duration play a significant role, I found it odd that the study used 3 time studies that all equal a greater than average time under duress than you normally see in such strength exercises.