Fitness & longevity glossary

Plain-English definitions of the training, nutrition and longevity terms used across the site. Each entry explains what it means, why it matters, and links to the calculators that put it to work.

• ApoB (Apolipoprotein B)

  A marker of the number of atherogenic particles in your blood.

• Autophagy

  The cell's recycling process that clears and reuses damaged components.

• BMR (Basal Metabolic Rate)

  The calories your body burns at complete rest just to stay alive.

• Deload

  A planned easier period to shed fatigue and allow recovery.

• DOMS (Delayed-Onset Muscle Soreness)

  The muscle soreness that appears a day or two after unfamiliar or hard exercise.

• Energy balance

  The relationship between calories consumed and calories expended.

• HRV (Heart Rate Variability)

  The variation in time between heartbeats, used as a readiness and recovery signal.

• Hypertrophy

  The growth of muscle fibres in size, the goal of most physique training.

• Insulin sensitivity

  How responsive your cells are to insulin — central to metabolic health.

• Lactate threshold

  The intensity above which lactate accumulates faster than the body can clear it.

• Lp(a) (Lipoprotein(a))

  A largely genetic, independent risk factor for cardiovascular disease.

• Mechanical tension

  The force a muscle produces under load — the primary driver of muscle growth.

• Muscle protein synthesis (MPS)

  The process of building new muscle protein, stimulated by training and protein intake.

• NEAT (Non-Exercise Activity Thermogenesis)

  Calories burned through everyday movement outside of formal exercise.

• One-rep max (1RM)

  The most weight you can lift for a single rep of an exercise.

• Periodisation

  Structuring training into phases to manage fatigue and peak performance.

• Progressive overload

  Gradually increasing the demand on a muscle over time so it keeps adapting.

• RIR (Reps in Reserve)

  How many more reps you could have done — a way to gauge proximity to failure.

• RPE (Rate of Perceived Exertion)

  A 1–10 scale for how hard a set felt, used to regulate training intensity.

• TDEE (Total Daily Energy Expenditure)

  The total calories you burn in a day, from all activity and metabolism.

• Training volume

  The total amount of work done, often counted as hard sets per muscle per week.

• VO₂max

  The maximum rate at which your body can use oxygen — a key marker of aerobic fitness.

• Zone 2

  A moderate aerobic intensity you can sustain while holding a conversation.