Hello all and welcome to post 46 of Strength & Conditioning For Therapists. What to focus on today? Well as you can tell from the title it’s Isometrics; Isometrics For Strength Training; Good or Bad ? I’m really fortunate to receive e-mails every day from therapists from around the globe asking me questions about strength and conditioning, and I’m delighted to answer them. One thing that tends to crop up frequently is the topic of isometric muscle contractions. In fact more so over the past couple of months, probably as we’re limited in what we can do to load musculature and create adaptations.

So let’s dive in.

What Are Isometric Muscle Contractions?

So, I have a little issue with the term isometric. Why, isometric basically means same length. Look it up in the dictionary and you’ll see something like:

“Relating to or denoting muscular action in which tension is developed without contraction of the muscle.”

(contraction here means muscle shortening)

We’re saying that during isometric muscle activation, there’s no change in muscle length….when in fact there is. Granted, it’s small, but it does happen. Sometimes you don’t even need imaging to see it. I prefer to use the word ‘static’ to describe these muscle contractions. However, let’s not be pedantic, the term isometric is commonly used, let’s define it as where ‘no appreciable external movement occurs’. 😉

Isometrics For Strength Training

So, in the absence of access to resistance equipment and closure of gyms is it worth thinking about isometric training? Bottom line, yes! I say yes with a caveat, we need to ensure the dose is right. But as a modality to promote strength gain, there’s lots of evidence. Furthermore, isometric training can be effective in effecting change in muscle size – hypertrophy.

Optimally Dosing Isometrics: How Long, What Intensity?

Take to Google for this and you’ll get all sorts of answers. Usually anywhere from 10 second upwards and often without much about intensity. So let’s break this down. What length of contraction is best?

Think about it …. If we want to optimise strength development … we want to optimise fast twitch muscle fibre / motor unit recruitment. Remember the characteristics of fast twitch fibres? Yup, they’re fatiguable!

We want to AVOID fatigue. If we think about energy systems and reflect on sustained MVC (maximal voluntary contraction) data, the length of the contraction should be less than 10s, which brings me to intensity. To what level (% of maximum) should we activate the musculature? Again, we want to as much as possible activate the fast twitch capacity of the muscle. As such 50% of maximal isn’t going to cut it. Look at the studies and you might get a decent response at 70% MVC, but the generally the greater the intensity, the greater the strength gain.

Let me say here that there is some debate in the literature. Some authors have found greater strength gains with higher intensities, and others haven’t, and there’s a similar debate for muscle hypertrophy. Given the variability in methodological approaches, it’s difficult to make direct comparisons. But…

  • if we understand the basic physiology we can make reasonable judgements
  • consultation of quality reviews on the topic can aid our decision making (There’s a nice little review just out by Lum & Barbosa on isometric training and performance (I’m afraid it’s behind a paywall))
  • don’t forget the principle of specificity!

Consolidating The Evidence

During dynamic resistance training programmes, higher intensity contractions promote greater gains in muscle strength vs. lower intensity – remember the optimal range for strength is 3-5RM (see here for a post on this topic). Whilst there might be a slightly reduced metabolic demand during isometric compared to concentric contractions (Beltman et al. 2004), and thus the potential to hold for longer before fatigue sets in, we still need to optimise recruitment from the fast twitch motor unit pool to achieve the best strength gains. Therefore, opting for high-intensity (>70% MVC), short duration contractions (<10 seconds) are likely to elicit good strength gains.

Indeed I’d go as far to suggest 3-5s contractions at 100% MVC

Think about the specificity of the training stimulus – would a low intensity sustained muscle endurance type protocol promote optimal strength gains …?

The principle of specificity is nicely illustrated in isometric training in a paper by a former colleague & co author. Tillin & Folland (2014) trained two groups of males. Participants either completed either MST (maximal strength training) or EST (explosive strength training) for 4 weeks. Participants were instructed to: contract as fast and hard as possible for ~1 s (EST); or contract progressively up to 75 % MVC and hold for 3 s (MST).

The instruction “hard and as fast as possible” cues participants to rapidly activate the musculature and thus recruit the fast twitch units from the off.

After training, the strength increases were greater in the MST compared to the EST group (21% vs. 11%, respectively); but early phase explosive force (at 100 ms) increased following EST (16%) and not in the MST group. The specificity of the EST group was such to improve explosive force production over a very short time period, whereas MST elicited maximal force gain.

“…short duration maximal contraction method seems to be a more time efficient method as compared to submaximal contraction method of varying duration.”

Lum & Barbosa (2019)

What Joint Angle?

Okay, so we’ve got an idea about intensity and duration, but what about the joint angle? This depends on the goal of the intervention and whether or not your client/patient is symptomatic or has any clinical restraints.

For example, is the goal of your isometric training to improve strength or function at a particular angle? This might relate to performance or a position of particular ‘weakness’ If so, there’s plenty of evidence for specificity of maximal gain at positions near to the trained angle, even in multi-joint exercises.

Specificity of Joint Angle

A recent paper by Bogdanis et al (2019) investigated the effects of low-volume maximal isometric leg-press at long (knee angle: 85° ± 2°) and short (knee angle: 145±2°) muscle lengths, combined with plyometric jumps. Intervention: 5–7 sets of 3s maximum isometric leg press exercise, 4 min recovery.

Results (see below) showed that training at shorter muscle tendon unit lengths, resulted in a large increase of maximal isometric force (22–58%), MIF below, and rate of force development (18–43%) specifically at the knee angles close to the training angle. These data suggest angle specificity for development of muscle force characteristics.

Isometrics With Patients?

Clinical populations often have restrictions, such as pain at particular joint positions. What happens of you need to increase muscle strength but you can’t train across the range? Interestingly, the authors found that whilst training at long muscle tendon unit lengths (knee angle: 85±2°) resulted in only a moderate improvement in muscle force (~12%), similar increase in strength were observed all knee angles, (see below).

What’s the relevance of this? Well, rehabilitating strength isometrically at long muscle lengths will likely have a beneficial effect across a range of joint positions. Whoop! This isn’t new, I’ve taught this as a strategy for years. Here’s another paper that illustrates the concept. Ultimately, there’s no need to change the specificity of the intervention by decreasing load, keep the intensity high and perform isometrically at a long muscle length.

Reps & Sets For Isometric Training

Right, let’s sum all of this up and get some take-homes for practice. A lot to summarise and consider, but if we’re interested making strength gains the priority then I reckon following the below principles you won’t go far wrong:

Dosing isometrics for strength gain

LOOK OUT!

I’m so excited to tell you that I’m launching the Get Back To Sport Academy….really soon. Keep your eyes peeled for all the details and announcements.

References