Isometric exercise

Isometric exercise is exercise in which a muscle produces force without changing length, so the joint it crosses doesn’t move. In physiology, contraction and shortening are not the same thing: a muscle can build tension while staying the same length, as when you hold a dumbbell in one position or a sleeping child in your arms (Gash et al., 2023). Planks, wall squats and pressing against something that doesn’t give are all isometric.

The opposite kind, where the muscle shortens or lengthens as the joint moves, is called isotonic or dynamic exercise. Many studies below compare the two.

Why isometric exercise suits a desk day

Isometric work needs no equipment and very little space, and the joint stays still, so it can sometimes be done when moving a sore area is uncomfortable. In the small tendon study described below, the athletes could do the isometric contractions without pain (Rio et al., 2015). That makes it one option among the short bursts of activity described in What are exercise snacks? and the microbreaks guide. It builds strength in a fixed position, which is different from stretching; the trade-off is discussed in Stretching or strengthening?

What does isometric exercise do for blood pressure?

This is where the evidence is strongest. A network meta-analysis of 270 randomised trials with 15,827 people compared types of exercise training. Isometric training lowered resting blood pressure by 8.24/4.00 mmHg on average, against 4.49/2.53 mmHg for aerobic training, and ranked first for lowering systolic pressure. The isometric wall squat was the most effective single type (Edwards et al., 2023).

A separate review of 24 trials in 1,143 adults with high blood pressure found reductions of about 7/4 mmHg in the clinic. Adverse events were rare, around one per 38,444 exercise bouts, but the authors rated the certainty of the evidence as low to very low (Hansford et al., 2021).

Does isometric exercise reduce pain?

The idea took off with a 2015 study of six volleyball players with painful knee tendons. A single bout of isometric contractions cut their pain during a squat test from 7.0 to 0.17 out of 10, and the effect lasted at least 45 minutes; moving (isotonic) contractions helped less (Rio et al., 2015). Six people is a very small study, and later reviews were less impressive:

• Tendon pain. A review of 10 trials across knee, shoulder, elbow, Achilles and hip tendons found, on limited evidence, that isometric exercise was not better than isotonic exercise for long-lasting tendon pain, either straight after treatment or over the following 12 weeks. Responses varied a lot between people (Clifford et al., 2020).
• Pain sensitivity. In pain-free people, exercise reliably dulls pain sensitivity for a while. A review of 13 studies with 346 people with local musculoskeletal pain found no consistent sign of that effect after isometric exercise (Bonello et al., 2021).

Isometric exercise for the neck

In a trial of 41 people with chronic neck pain, one group did isometric neck exercises and the other did craniocervical flexion training, which targets the deep neck flexors, for eight weeks. Both groups improved in pain, disability, endurance and range of movement, but the craniocervical flexion group improved more on most measures (Chung & Jeong, 2018). Exercises aimed at the front of the neck are collected under forward head posture exercises.

Who should be careful?

The trials in people with high blood pressure reported very few problems, but with low certainty (Hansford et al., 2021). If you have heart disease or blood pressure that isn’t well controlled, ask your GP or practice nurse before starting a training programme. As with any exercise, stop if it causes sharp or worsening pain.