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Time under tension (TUT) for muscle growth

During the COVID lockdown many of my clients have continued training from home with me via Zoom. They mostly have their own equipment but still, it doesn’t provide the unlimited weight option of the gym. Accordingly we have had to adapt our training and find ways to maximise the muscle building signalling response from our training. This has mainly been focused on blood flow restriction training and/or extensive pre-exhaust isolation work, prior to compound lifts to help simulate heavier loads.

During the compound movements we have focused on achieving a certain TUT. (TUT is the time a muscle remains under tension during a set, i.e 10 reps of squats with a 2 second eccentric (muscle lengthening) and 2 sec concentric (shortening) phase would mean 40 sec total TUT). We know from scientific studies that TUT is a driver for muscular hypertrophy (muscle growth) along with volume, mainly due to lactic acid, but it appears to be a less efficient process than consistently adding weight to the bar for more reps. Ergo, the good old fashion plain and simple method of getting stronger within a given rep range.

What is the main stimulus for muscle growth?

As alluded to, the main stimulus is, getting stronger for increased reps. It can be explained like this.

Muscle fibre recruitment + Mechanical stress on these fibres x reps = HYPERTROPHY STIMULUS.

Fibre recruitment can be improved by either lifting heavier weights relative to your max or creating pre-fatigue, meaning muscles are already tired and capable of less work.

Mechanical stress on a muscle fibre is created by tension under load and the stretch and squeeze of a muscle throughout its range of motion (ROM).

A bit of context may be useful at this point. A muscle contracts by way of the sliding filament theory. A muscle fibre consists of two proteins, actin and myosin. During contraction the two proteins slide together, shortening, overlapping and creating a temporary bridge. This provides strength whilst the muscle remains in its contracted state. When a muscle is lengthened under tension whilst still trying to maintain contraction (shortening) it produces mTOR. This enzyme creates a signalling pathway to create more muscle. Hence why you are encouraged to contract against the weight (for muscle building purposes, power lifting is different). This is because the actin-myosin bridge created through muscular contraction can only shorten a muscle. The resistance of a weight is trying to lengthening the muscle and the two opposing forces create mechanical stress.

Therefore, just letting a weight drop under gravity is inefficient for mechanical tension and subsequent mechanical stress. Best strategies for maximising your mechanical stress are contracting as hard as you can during the lift, keep rep speed constant (too much speed creates momentum making the lift easier and decreasing force required) and training a full ROM to maximise the lengthening and stretch of the fibre.

Difference between TUT and classic overload:

This is why TUT, whilst a useful tool, cannot match the effectiveness of fibre recruitment + mechanical stress x reps. The number of times (ie reps) that your stretch and contract a muscle fibre has a huge effect on the release of mTOR.  Compare this to TUT work and it is clear that you will fatigue before as many reps are completed. This is far less effective, although as discussed earlier not pointless, (and still highly valid in many cases.)

So, you may logically say, drop the resistance to hit the rep range and maximise our TUT. Unfortunately, in this instance you won’t get the same degree of fibre recruitment with a lighter weight as per the first part of the equation. BUT, if the intensity is sufficient to reach failure inside 40-50 secs you will still provide plenty of muscle building stimulus without as heavy a starting weight. This is exactly why we train both slowly and intensely from home. Of note, if you are still a fair way from your muscle mass genetic maximum you can still progress nicely with this method. (Albeit in my experience slightly less efficiently than with ‘unlimited’ gym weight.)

TUT has its place:

TUT DOES have its place. Whilst advanced trainee are unlikely to progress with this method, the chances that you fall into this demographic are low. Most people will still continue developing at a slighter slower rate. This is still a great deal more productive than following a televised body-weight circuit.  Older clients, or people with impaired recovery can also benefit from TUT work. Done on isolation exercises (that don’t load the eccentric/lengthening  portion fully) over 40-60 secs can provide slow and steady results without too much muscle breakdown associated with the standard heavier weight for more reps standard protocol.


For absolute best results, muscle fibre recruitment + mechanical stress x reps is the superior way to gain muscle. That said, TUT is a perfectly valid method to use in situations where you cannot access heavy weights. It will build muscle in most. It will also prevent muscle loss in all populations if away from the gym for an extended period of time.

I hope you enjoyed this. Do get in touch if you need any help with your own fitness goals.