Exercise Intensity and Dosing

The UK Chief Medical Officers updated their physical activity guidelines in July 2026. The headline numbers are unchanged: adults aged 19 to 64 should accumulate at least 150 minutes of moderate intensity activity a week, or 75 minutes of vigorous intensity activity, or shorter durations of very vigorous activity, or a combination, alongside muscle strengthening on at least two days a week and minimising sedentary time, with daily activity still encouraged even where the weekly target is concentrated into fewer sessions. What has changed is the emphasis and several points of practical detail that matter when prescribing.

Four are worth knowing. First, the 150 minutes can be accumulated in bouts of any length, and can even be achieved in one or two sessions across the week while retaining the benefit, so the old minimum bout of ten minutes has gone. Second, light intensity activity is given far more prominence, because the evidence suggests its benefits can match those of moderate activity if performed for longer, which matters for anyone who cannot reach moderate intensity. Third, on strength, measurable benefit is described from over 30 and up to 120 minutes of muscle strengthening a week, though the evidence is not strong enough to specify a duration, and the benefits are greatest when combined with aerobic activity. Fourth, and new, the guidelines address glucagon-like peptide-1 agonist weight management drugs: because both fat and muscle are lost on these agents, strengthening activity is likely to be particularly important for preserving muscle mass, and the drugs are licensed only alongside physical activity and behavioural change.

Two framing principles run through the document and are examinable in their own right. Some is good and more is better, with the steepest gains made moving from inactive to slightly active rather than from active to very active. And the benefits of activity outweigh the risks for almost everyone, including people living with long term conditions, who often have the most to gain.

Intensity is expressed either in absolute terms, meaning the energy cost of the activity itself, or in relative terms, meaning how hard it feels for that individual. Both have a place, and confusing them is a common error.

The metabolic equivalent of task (MET) is the standard absolute measure. One MET is the energy cost of sitting quietly, taken as an oxygen uptake of about 3.5 mL/kg/min, so an activity of four METs costs roughly four times that reference value. The 3.5 figure is an assigned convention, and measured resting metabolic rate varies substantially between individuals. Light activity is below three METs, moderate is three to under six, and vigorous is six or more. The limitations matter: MET values assume a reference adult, use total body mass without regard to composition, tend to overestimate true resting expenditure, and take no account of age, fitness or disease. A brisk walk that is moderate for a fit 30 year old may be vigorous for a deconditioned 80 year old, and the MET value does not change.

Relative measures solve that problem. Rating of perceived exertion (RPE) exists in two versions and candidates routinely muddle them. The original Borg scale runs from 6 to 20, chosen so that multiplying by ten approximates heart rate in a healthy young adult, and on it light activity is about 9 to 11, moderate 12 to 13, vigorous roughly 14 to 17, and very hard or near-maximal 18 to 20. The modified Borg category-ratio scale runs from 0 to 10, where light is roughly 2 to 4, moderate 5 to 6, and vigorous 7 to 8. Always state which scale is being used. The talk test is the simplest relative measure and is the one UK guidance highlights: being able to talk but not sing indicates moderate intensity, while difficulty talking without pausing indicates vigorous. Heart rate methods sit between the two. Percentage of maximum heart rate is crude, whereas heart rate reserve (HRR), calculated with the Karvonen method as resting heart rate plus a target percentage of the difference between maximum and resting heart rate, incorporates resting heart rate and usually individualises intensity better than a percentage of estimated maximum. Broadly, moderate activity is 40 to 59% of heart rate reserve, vigorous is 60 to 89%, and 90% or above is near-maximal. These remain broad prescription zones rather than exact physiological thresholds.

Resistance training is dosed across several parameters rather than load alone: intensity or load, sets and repetitions, weekly frequency, proximity to failure, exercise selection and rest intervals. UK guidance asks for activities using all the major muscle groups, upper and lower body, on at least two days a week, and explicitly accepts bodyweight work, free weights, resistance machines, elastic bands and loaded daily tasks such as stair climbing or carrying. Load is conventionally expressed as a percentage of the one repetition maximum (1RM), the heaviest load that can be lifted once with good technique. Endurance-oriented work uses lighter loads for higher repetitions, hypertrophy work sits in the middle, and maximal strength work uses heavy loads for few repetitions. Where a true 1RM is unsafe or impractical, a repetition maximum at a lighter load can be used to estimate it, or the set can simply be prescribed by proximity to failure. It is worth telling patients that the first four to six weeks of gains are predominantly neural, through better motor unit recruitment and reduced antagonist co-activation, rather than through muscle growth, so visible change lags behind real improvement. Hypertrophy and connective tissue adaptation are nonetheless already developing over the same period.

Aerobic work comes in three formats. Moderate intensity continuous training is steady work at a sustainable level. High intensity interval training (HIIT) uses repeated vigorous or near-maximal work intervals separated by recovery, often cited around 85 to 95% of maximum heart rate, though protocols vary substantially. Sprint interval training uses repeated all-out or supramaximal sprints with relatively long recovery. Some work-matched mechanistic studies show a stronger mitochondrial stimulus from interval exercise, and some low-volume protocols improve maximal oxygen uptake with less exercise time, but total session time including warm-up and recovery, tolerability and adherence all erode the apparent time advantage, and clinical differences vary by population and protocol. Evidence supports cardiorespiratory benefit from intervals in selected older adults, while remaining less certain in frailty, multimorbidity and unsupervised practice.

Progression is where prescriptions fail. For inactive or clinically vulnerable people the usual approach is to build duration and consistency first, then progress intensity according to goals, symptoms, recovery and risk. Change one variable at a time. Rapid changes in exposure may contribute to symptoms, but injury risk reflects the interaction between current exposure, tissue capacity, recovery, previous injury and the activity itself. For someone starting from inactivity, a short, frequent, low-intensity prescription that is actually completed beats an optimal one that is abandoned, and small specific targets are legitimate stepping stones toward the guideline level rather than a failure to reach it.

Heart rate is the intensity measure most likely to mislead, and recognising when is a recurring exam point. The age-predicted maximum of 220 minus age carries wide individual error even in health, and becomes unsuitable whenever medication, rhythm or pacing alters the chronotropic response. Beta blockade, atrial fibrillation, autonomic neuropathy and some paced rhythms all make generic heart rate zones unreliable, although an individually measured response may still be clinically useful. Generic targets are likewise a poor fit in children and in pregnancy, where resting heart rate rises physiologically. Where generic zones are unsuitable, prescribe and monitor by perceived exertion or the talk test.

• •One metabolic equivalent is about 3.5 mL/kg/min; light is under three, moderate three to under six, vigorous six or more.
• •State which perceived exertion scale you mean: original Borg runs 6 to 20, the modified category-ratio scale runs 0 to 10.
• •The talk test is the UK guidance marker: talk but not sing is moderate, difficulty talking is vigorous.
• •Heart rate reserve and the Karvonen method account for baseline fitness; percentage of maximum heart rate does not.
• •For inactive people, build duration and consistency before progressing intensity, changing one variable at a time.
• •Generic heart rate zones are unsuitable where medication, rhythm or pacing alters the response; use perceived exertion.