| Recommended weekly aerobic activity (adults) | 150–300 min moderate-intensity or 75–150 min vigorous-intensity (U.S. Department of Health and Human Services Physical Activity Guidelines, 2018) |
| Muscle-strengthening recommendation | 2 or more days per week (U.S. Physical Activity Guidelines for Americans, 2nd edition) |
| Typical HIIT session duration | 15–30 minutes (General clinical and research convention) |
| RPE scale range (Borg scale) | 6 (no exertion) to 20 (maximal exertion) (Gunnar Borg, original scale design) |
| Average sedentary adult VO2 max | Approximately 30–40 mL/kg/min (General population reference range, varies by age and sex) |
Why Fitness Jargon Can Feel Like a Barrier
Walk into any gym, browse a workout app, or read an exercise article and you'll quickly run into a wall of abbreviations and technical terms. HIIT, RPE, VO2 max, progressive overload — these phrases get used as though everyone already knows what they mean. When they go unexplained, they can make physical activity feel more complicated and exclusive than it actually is.
This reference guide cuts through that noise. Each term below is defined in plain English, with enough context to understand how it applies to real movement — whether you're just starting out, returning after a break, or simply want to understand what a trainer or class instructor is talking about. If you're exploring what counts as physical activity in the first place, our companion piece on walking as exercise is a good place to start.
Aerobic Exercise
Physical activity sustained for an extended period that relies primarily on oxygen to produce energy. Examples include running, cycling, and swimming. Often called 'cardio,' it supports heart and lung health.
Anaerobic Exercise
High-intensity activity performed in short bursts where the body's demand for oxygen exceeds supply, relying instead on stored energy. Sprinting and heavy resistance training are common examples.
HIIT (High-Intensity Interval Training)
A training method that alternates short periods of intense effort with brief recovery intervals. Sessions are typically time-efficient, and research suggests HIIT can improve cardiovascular fitness and metabolic health.
RPE (Rate of Perceived Exertion)
A self-reported scale used to estimate exercise intensity based on how hard an activity feels. The most common version runs from 6 to 20, though a simplified 1–10 scale is widely used in everyday fitness contexts.
VO2 Max
The maximum volume of oxygen your body can use during intense exercise, expressed in milliliters per kilogram of body weight per minute. It is widely used as a marker of cardiorespiratory fitness.
Progressive Overload
The principle of gradually increasing training demands — such as resistance, volume, or intensity — over time so that the body continues to adapt and improve.
Reps and Sets
A 'rep' (repetition) is one complete movement of an exercise; a 'set' is a group of consecutive reps. For example, three sets of ten reps means performing an exercise ten times, resting, and repeating that cycle twice more.
MET (Metabolic Equivalent of Task)
A unit that estimates the energy cost of physical activities relative to rest. An activity with a MET of 4 requires roughly four times the energy of sitting quietly. It is used in research and public health guidelines.
Active Recovery
Low-intensity movement performed on rest days or between harder sessions — such as walking, gentle yoga, or light cycling — to promote circulation, reduce muscle soreness, and support overall recovery.
1RM (One-Rep Max)
The maximum amount of weight a person can lift for exactly one full repetition of a given exercise. It is used to calculate appropriate training loads, often expressed as a percentage in programming guidance.
Functional Movement
Exercises that train movement patterns used in everyday life — such as squatting, hinging, pushing, and pulling — rather than isolating individual muscles. Associated with improved balance, coordination, and injury prevention.
Hypertrophy
The increase in muscle size that results from resistance training. Hypertrophy-focused programs typically use moderate weights with higher repetition ranges and controlled rest periods to maximise muscle growth stimulus.
Key Concepts Behind Exercise Programming
Understanding a handful of foundational principles helps make sense of almost any workout plan you'll encounter.
| Recommended weekly aerobic activity (adults) | 150–300 min moderate-intensity or 75–150 min vigorous-intensity (U.S. Department of Health and Human Services Physical Activity Guidelines, 2018) |
| Muscle-strengthening recommendation | 2 or more days per week (U.S. Physical Activity Guidelines for Americans, 2nd edition) |
| Typical HIIT session duration | 15–30 minutes (General clinical and research convention) |
| RPE scale range (Borg scale) | 6 (no exertion) to 20 (maximal exertion) (Gunnar Borg, original scale design) |
| Average sedentary adult VO2 max | Approximately 30–40 mL/kg/min (General population reference range, varies by age and sex) |
Progressive overload is the engine behind almost every structured training program. It simply means gradually increasing the challenge placed on your body — through more weight, more repetitions, less rest, or greater range of motion — so that your muscles and cardiovascular system continue to adapt. Without it, progress tends to plateau.
Recovery is equally important and often underestimated. Muscle repair, strength gain, and cardiovascular adaptation happen during rest, not during the workout itself. Rest days, adequate sleep, and active recovery (light movement like walking or gentle stretching) all serve this function.
For a deeper look at how flexibility and mobility fit into a well-rounded program, see our guide on flexibility, mobility, and stretching. These terms describe related but distinct physical qualities, and confusing them can lead to gaps in training.
Priorities and appropriate intensity also shift over time. Adults in their 50s and beyond will find relevant context in our overview of fitness after 50.
These Guidelines Are a Starting Point, Not a Prescription
Public health activity guidelines reflect population-level recommendations, not individualized targets. Your appropriate starting point depends on your current fitness level, health history, and any conditions you may have. A certified exercise professional or your healthcare provider can help translate these general benchmarks into a plan that fits your circumstances.
This article is for general informational purposes only and does not constitute medical advice. Consult a qualified healthcare professional before beginning a new exercise program, particularly if you have an existing health condition, injury, or are returning to activity after a long break.