Isometric training for muscle growth - Isometrics Part 1

If you would have asked me 6 months ago how interested I am about isometric training the answer would have been quite different. The truth is that I have never looked into isometric training before because dynamic movements are superior in building strength and muscle.

But since I faced some shoulder issues and developed tendonitis on the long head of the bicep (caused by the nerve damage I have) I had to let go of some of the dynamic movements since they irritate the tendon quite a bit. In order to rehab my joints and tendons I got interested on how to maintain my current physique and strength level with isometric training.

Doing a quick (or extensive) online search does not provide much tips on how to exactly use isometrics to gain muscle and strength. Most descriptions are quite vague and provide only minimal information. The basic instructions for isometric holds go like this without any further information: Do a hold for 30-60seconds. Rest and repeat. That's it. But I didn't find any volume recommendations or other aspects of training. For example how isometric hold times compare to dynamic repetitions (hold times vs rep ranges). This is a topic where we return in part 2.

I would like to point out that this article is mainly about yielding isometrics (holding a weight or a loaded position) and not overcoming isometrics (trying to move an Immovable object). But basically the same principles would apply to overcoming isometrics. The problem that I have with overcoming isometrics is that it is quite difficult to measure your progress and force production. You don’t exactly know if your force output is increasing without using other ways to measure progress. Also I like to train with less intense isometric holds instead of 100..120% that the overcoming isometrics can provide. But they do have a great potential to improve tendon health by safely overloading the tendons at a safe angle.

Support hold (specially if you use rings set wide) works the chest to a great degree even if its not working the target muscle in long muscle length

How concentrics, eccentrics and isometrics compare for muscle building

If you placed dynamic movements and isometric holds in order according to muscle and strength building capability you will get the following:

1. Concentric + eccentric (Muscle shortens and lengthens under load. Positive + negative part of the movement) 
2. Eccentric (Muscle lengthens under load, negative part of the movement)
3. Concentric (Muscle shortens under load, positive part of the movement)
4. Isometric (holding the same position)

Now why should you even bother with isometrics? If you have no limitations in your training capability the benefits of isometric training are minimal compared to dynamic movements. But they do have an application in normal training routines that revolves around dynamic movements. For example, paused reps are one form of isometrics where you emphasize a certain part of the movement pattern such as the bottom of a squat.

Now where isometrics would come into play and make a huge difference would be a situation where you are limited in the exercise selection you can perform due to an injury. This would be a situation where you get no training stimulus vs some training stimulus. Isometrics have the benefit of training muscles at a certain angle which can be selected in a way that it does not produce pain or make the current condition worse. For example someone who is recovering from shoulder impingement, tendonitis or surgery has to limit the range of motion in most cases. So for example in some cases all exercises where you push or pull above your shoulder level are out of the question. Also any movement of the joint might cause pain if you have painful tendons since the tendons usually have to slide across the bone surface when performing dynamic exercises. 

What research has to say about isometrics?

There was one extensive piece of research that I stumbled upon. “Isometric training and long-term adaptations: Effects of muscle length, intensity, and intent: A systematic review”. 

Basically this paper bundles many isometric training studies in one.

Here is a youtube video referencing this research if you are interested:

https://www.youtube.com/watch?v=Fh13SDYSF3E

And here is the whole paper:

https://www.researchgate.net/publication/329881153_Isometric_training_and_long-term_adaptations_Effects_of_muscle_length_intensity_and_intent_A_systematic_review

The key points from this research with quotes:

Training at long muscle length is better for hypertrophy

Isometric training at longer muscle lengths produced greater muscular hypertrophy when compared to equal volumes of shorter muscle length training.

Hypertrophy response with long muscle length training is 2x compared to short muscle length training when volume is matched!

Isometric training at longer muscle lengths (0.86%‐1.69%/week, ES = 0.03‐0.09/week) produced greater muscular hypertrophy when compared to equal volumes of shorter muscle length training (0.08%‐0.83%/week, ES = −0.003 to 0.07/week).

Both high intensity and low intensity improve muscle hypertrophy

Substantial improvements in muscular hypertrophy and maximal force production were reported regardless of training intensity. 

When volume is equated training at LML is superior to SML training for hypertrophy, due to higher quantities of muscle damage and metabolite buildup. (Take note that long muscle lenghts are more effective when volume is EQUATED. But it is not necessary to equate volume in your training. If you use mid range or short muscle lengths you can use more training volume to reach the same training effect. This can be done by increasing the training volume by 20..50% for example compared to long muscle lengths.)

Of the studies comparing isometric training at differing joint angles, only three evaluated muscle volume or thickness. All three studies found that isometric training at long muscle lengths (LMLs) was superior to equal volumes of training at short muscle lengths (SMLs) for increasing muscle size. These findings are not surprising as a large portion of the existing literature has demonstrated that dynamic training through a large range of motion is beneficial when hypertrophy is desired. Additionally, contractions at LML tend to produce higher quantities of

muscle damage, likely by altering the joint moment arm and increasing mechanical tension when compared to a SML. Contractions at LML also result in greater blood flow occlusion, rates of oxygen consumption, and metabolite buildup when compared to SML contractions.These metabolic factors are well established to contribute to muscular hypertrophy.

No significant difference between 60% and 100% intensity when training volume is matched

Similarly, Kanehisa et al employed ten weeks of volume‐equated isometric training at either low (60%) or high (100%) intensity. While both low‐ and high‐intensity training programs significantly increased triceps brachii hypertrophy, there was no statistical between‐group difference in anatomical cross‐sectional area. However, high‐intensity training had a greater effect on muscle volume than the lower intensity despite nearly identical effect sizes. These findings are in close agreement with recent studies and meta‐analyses that concluded that hypertrophic adaptations are similar if total load is equated and training intensity is >20% of maximal voluntary contraction.

Note: Protocol they used was: 4x30sec (60%) and 12x6sec (100%) !!!

Higher training volume is better than lower volume for hypertrophy

When the training volume is not equated between groups, it seems higher volumes are better for inducing muscular hypertrophy, regardless of contraction intensity. Meyers compared low (3×6 seconds MVIC)‐ and high (20×6 seconds MVIC)‐volume isometric training of the elbow flexors.

Following the six‐week intervention, the high‐volume training program resulted in significantly greater improvements in muscle girth compared to the low‐volume group 

Maximum strength contractions produce more hypertrophy than explosive reps

Similarly, Balshaw et al and Massey et al compared “maximal strength” (40×3 seconds contractions, 75% of MVIC) and “explosive” (40×1 seconds contractions, 80% of MVIC) isometric training. Following the 12‐week interventions, the “maximal strength” training groups experienced significant improvements in quadriceps muscle volume, whereas the “explosive” training groups did not.Furthermore, the difference between groups was statistically significant 

Long duration isometrics results in greater hypertrophy even if time under tension is matched

Interestingly, Schott,McCully, and Rutherford found that long‐duration (4×30second MVIC) contractions resulted in greater hypertrophic adaptations when compared to short (4sets×10×3 second MVIC)‐duration contractions despite total time‐under‐tension being equated between groups. Following 14 weeks, the long‐duration contraction group significantly improved vastus lateralis anatomical cross‐sectional area at the proximal (10.1%) and distal (11.1%) portions of the femur, whereas no significant hypertrophic adaptations were observed in the short‐duration group 

Schott, McCully, and Rutherford’s findings are somewhat surprising as both groups underwent the same time‐under‐tension. However, sustained contractions are known to restrict blood flow, reduce muscle oxygen saturation, and increase metabolite concentrations in the muscle stimulating hypertrophy via multiple local and systemic mechanisms. Additionally, muscle contractions at LML consume more oxygen, which may in part explain the advantage of LML training when muscular hypertrophy is the primary goal.

You improve the neuromuscular function around the angle you train at but this does not significantly impact dynamic performance. So the best approach is to train for muscle size and improve overall performance.

The long‐held belief that isometric resistance training should occur at the most important angle present in a dynamic activity holds true as the largest improvements in neuromuscular function occur at the trained angle.However, large neurological discrepancies exist between isometric and dynamic movements suggesting that static training may not be an effective strategy for directly improving sports performance and should be primarily employed to alter morphology. Therefore, isometric training should occur predominantly at relatively LMLs as there is a clear advantage for improving muscle volumes and strength throughout a range of motion.

Best approach to progress isometrics is to increase time under tension, total number of sets and training at longer muscle lengths

Therefore, increasing contraction durations, increasing total volume, or shifting to longer muscle lengths is likely more efficient means of progressing isometric resistance training if strength and muscle size are a priority. Conversely, high‐intensity (≥70% of MVIC) isometric contraction exclusively produced increased tendon thickness and stiffness. As overly compliant tendons are often an issue in untrained and injured populations, progressively increasing intensity during isometric contractions may be a safe and efficient means of preparing tendinous tissue for future dynamic loading.

High intensity is required to improve tendon health, structure and stiffness

High‐intensity (≥70%) contractions are required for improving tendon structure and function. 

Both investigations found increased Achilles tendon CSA and stiffness following high‐intensity , but not low‐intensity training. Furthermore, tendon elongation under stress (an indication of elasticity) increased following low‐intensity , but not high‐intensity training.

Additionally, the included studies only compared isometric training at ~55 and 90% of MVIC which leaves a large range of potential intensities. However, previous interventions have reported large increases in tendon stiffness following training between 70% and 100% of MVIC. Therefore, it might be that a minimum intensity of ~70% MVIC is required to induce meaningful changes in tendon thickness and stiffness.

From the keypoints above we can create a checklist when planning isometric training:

• Selected exercise trains target muscle in long muscle length. This is usually mid range for most exercises and for some exercises you can safely use a stretched position. But don’t do extreme stretches since they increase risk of injury. Also you need to avoid leaning into the joints at the end range. Select a position where the muscle has to actively contract against resistance and you don't get assistance from stretched tissues (for example you don't need much force to hold certain stretched positions such as the bottom part of a calf raise). 
• Hold time range 10-30+seconds. Doing short isometric holds does not effectively increase hypertrophy and make training harder and possibly increase risk of injury due to high intensity. Thus a range of 30-90 seconds could be useful to accumulate enough time under tension in a workout
• Select safe exercises to train close to failure without increasing injury risk. When you reach failure the joints should be protected. For example floor limits the range of motion for push-ups when failure point is reached but for dumbbell bench press the joints are compromised when reaching muscular failure since they can overextend under load.
• Selected exercises generate most of the fatigue on the target muscle and are not greatly limited by secondary muscle groups. Isolation exercises could work better compared to compound exercises.
• Can be done for multiple sets without generating too much overall fatigue (with good stimulus-fatigue ratio). For example barbell squat isometric will generate a significant amount of overall fatigue compared to leg press or single leg squat with similar load.
• Increase number of sets gradually to find your minimum effective training volume. If you are able to make progress in hold times and loads weekly or biweekly you are doing great. Since different isometrics load the target muscles at different rates effective training volume is expected to be in the range of 5-30 weekly sets depending on the exercise selection and training history. So it is difficult to make any general recommendations for weekly volume. It depends on the intensity (% of 1RM == tension) and muscle length in the selected exercise.

How to get sufficient training stimulus from isometrics only?

Remember how I placed movement patterns to a specific order based on the strength and muscle building capability and how isometrics were the last to finish. Looks bad doesn’t it? But it does not mean that isometrics cannot reach a similar stimulus going from not great to a decent level at least. And I think you already know the answer. Do more work to reach a similar training effect. Quite simple. We already know that you can make good strength and muscle gains with 8-15+ sets per week with dynamic exercises. So in order to make isometrics work we are looking at increasing this volume by at least 50% or by doubling it. That would be 12-30sets per week. Yikes! That is a lot of isometric holds to be done. With proper rest times you would end up doubling the time required for your workouts. But don’t worry there are well known ways to squeeze more work into a short time frame. For example drop sets, rest pause sets, super sets, myo reps etc. Personally I would aim somewhere halfway of that training volume and increase or decrease the number of sets based on progress. So about 15-20 weekly isometric sets should be plenty but not too much.

Rest pause isometric sets

If you have selected safe exercises the best way to incorporate more training volume in a short period of time would be rest pause sets (similar to Myo rep training protocol) where you train a set close to failure (15-30 reps), rest for about 10-15 deep breaths, do a second set close to failure (about 3-5reps), rest 10-15 breaths and repeat for total 5 mini sets or more. 

For isometrics a similar protocol would be: 

Almost max hold in the range of 30-90seconds rest for 10 breaths, another almost max hold, rest and so on until you reach 5 mini sets. Now one hard rest pause set equals around 3-5 straight sets depending on the effort. Lower end if you don’t train to complete muscular failure. So for example if you do 5 isometric rest pause sets in total this would equal around 15 separate sets. 

How to do an isometric rest pause set:

-Set 1: Almost max hold in the 30-90second range, Rest for 10-15 breaths

-Mini-set 1: Almost max hold close to failure (could be about 10-30seconds), Rest for 10-15 breaths

-Mini-set 2: Almost max hold close to failure (could be about 10-20seconds), Rest for 10-15 breaths

-Mini-set 3: Almost max hold close to failure (could be about 10-20seconds), Rest for 10-15 breaths

-Mini-set 4: Almost max hold close to failure (could be about 10-20seconds), Rest for 10-15 breaths

-Mini-set 5: Almost max hold close to failure (could be about 10-20seconds)

-Stop here or do more based on your programming

Increase training volume incrementally

When starting with isometrics and rest pause sets, increase the number of sets slowly like in all the other training methods. Start with straight sets only and incorporate rest pause sets when you are comfortable with the straight sets. Starting with fever rest pause sets at first and increasing the number of rest pause sets over time. So for example you might begin with 5 weekly straight isometric sets initially and over time change some or all the sets to isometric rest pause sets reaching about 20 sets total if we count one rest pause set to equal 4 straight sets.

General tips for isometric training - tracking hold times without stopwatch

You can track hold times using deep breaths instead of using a stopwatch for each hold. One deep breath equals around 2-3 seconds depending on the individual so you have to test how many deep breaths 60 seconds is. For me this value is around 27 deep breaths per minute that equals 2.3 seconds for a single breath. Don’t hyperventilate. Take calm deep breaths. For me the range of 30-90 seconds is about 15-45 deep breaths. Once I reach the top range of 45 breaths I increase the load or switch to a harder hold position or exercise depending if the exercise is weighted or bodyweight only.