Fitness & Health Glossary
Every fitness term you need to know, explained in plain English. Click any letter to jump to that section, or scroll through the full list.
1
1RM
One-Rep Max — the heaviest weight you could lift for a single repetition of a given exercise with good form.
A
ApoB
Apolipoprotein B — a protein found on LDL and other harmful cholesterol particles. Many doctors consider it a better predictor of heart disease risk than LDL cholesterol alone.
B
Basal Metabolic Rate
Often called BMR — the number of calories your body burns just to stay alive if you did nothing all day. It powers your breathing, heartbeat, and brain function.
Biological Age
An estimate of how old your body acts compared to your actual age. Someone who is 40 years old might have a biological age of 35 if they're very fit and healthy.
BMI
Body Mass Index — a simple number calculated from your height and weight that gives a rough idea of whether you're underweight, at a normal weight, overweight, or obese.
Body Fat Percentage
The portion of your total body weight that is fat tissue, expressed as a percentage. Essential fat is needed for health; excess fat increases health risks.
C
Calorie Deficit
Eating fewer calories than your body burns each day. This is what causes weight loss — your body uses stored fat to make up the difference.
Carbohydrates
Your body's main source of quick energy. Found in bread, rice, pasta, fruit, and vegetables. Your body breaks them down into glucose for fuel.
Cortisol
Your body's main stress hormone. It follows a natural daily rhythm — highest in the morning, lowest at night. Chronically high cortisol can affect sleep, weight, and immune function.
D
DHEA-S
Dehydroepiandrosterone sulfate — a hormone made by your adrenal glands. It naturally drops with age and is sometimes called an 'anti-aging' hormone.
E
Epley Formula
A formula that estimates your one-rep max from the weight and reps you actually lifted. It's most accurate when you use a weight you can lift for 2–10 reps.
Estradiol
The main form of estrogen. It plays a key role in bone health, heart protection, mood, and metabolism — especially important during perimenopause and menopause.
F
Fasting Insulin
The amount of insulin in your blood after an overnight fast. Elevated fasting insulin is one of the earliest signs of metabolic problems, often showing up before blood sugar rises.
Fat
A macronutrient that supports hormone production, brain health, and absorbing certain vitamins. Found in oils, nuts, avocado, butter, and fatty fish.
Ferritin
A blood protein that stores iron. Low ferritin can mean iron deficiency (very common in women); very high levels can signal inflammation or iron overload.
Fitness Age
An estimate of how old your body acts based on cardiovascular fitness, especially VO2 max. A fit 50-year-old might have the fitness age of a 35-year-old.
H
HbA1c
A blood test that shows your average blood sugar over the past 2–3 months. Lower levels are linked to better metabolic health and longer life.
Heart Rate Zones
Five ranges of heart rate intensity, from easy recovery (Zone 1) to all-out effort (Zone 5). Training in different zones builds different fitness qualities.
Homocysteine
An amino acid in your blood. High levels are linked to greater risk of heart disease, stroke, and cognitive decline. B vitamins help keep it in check.
hs-CRP
High-sensitivity C-reactive protein — a blood marker of inflammation in your body. Chronically high levels are linked to greater risk of heart disease and other conditions.
Hydration
Keeping your body properly supplied with water. Even mild dehydration can affect energy, focus, and exercise performance.
I
Intermittent Fasting
An eating pattern that cycles between periods of fasting and eating. Common methods include 16:8 (16 hours fasting, 8 hours eating) and 18:6.
K
Karvonen Formula
A method for calculating heart rate training zones that accounts for your resting heart rate, giving more personalized zone ranges than age-only formulas.
L
Lean Body Mass
Everything in your body that isn't fat — muscles, bones, organs, and water. A higher lean body mass relative to your weight usually means better fitness.
Life Expectancy
An estimate of how many years a person is likely to live based on current health, lifestyle, and statistical averages for their age and gender.
M
Macros
Short for macronutrients — the three main nutrients your body needs in large amounts: protein (builds muscle), carbohydrates (provides energy), and fat (supports hormones and organs).
Magnesium (RBC)
Red blood cell magnesium — a more accurate measure of your body's magnesium than a standard blood test. Magnesium is involved in over 300 processes in your body.
MET
Metabolic Equivalent of Task — a way to measure how hard an activity is. Sitting quietly is 1 MET; running is about 8–12 METs depending on speed.
Mifflin-St Jeor
A widely used formula for estimating how many calories your body burns at rest. It's considered one of the most accurate methods available without lab equipment.
O
Omega-3 Index
The percentage of omega-3 fats (EPA and DHA) in your red blood cell membranes. An index above 8% is linked to lower heart disease risk.
P
Protein
A macronutrient that helps build and repair muscles, skin, and organs. Found in meat, fish, eggs, dairy, beans, and tofu.
R
Resting Heart Rate
How many times your heart beats per minute when you're completely at rest. A lower resting heart rate usually means your heart is more efficient.
Running Pace
How long it takes you to cover a set distance, usually expressed as minutes per kilometer or minutes per mile. A faster pace means a lower number.
S
Sleep Cycles
Your brain goes through 90-minute cycles during sleep, moving from light sleep to deep sleep to REM (dreaming). Waking at the end of a cycle helps you feel refreshed.
Somatotype
A system for classifying body types into three categories: ectomorph (lean and long), mesomorph (muscular and medium), and endomorph (wider and softer).
T
TDEE
Total Daily Energy Expenditure — the total number of calories your body burns in a day, including exercise and just staying alive.
Triglycerides
A type of fat in your blood. High levels are linked to heart disease risk and are often a sign of insulin resistance or too much sugar and alcohol.
TSH
Thyroid-stimulating hormone — a marker of how well your thyroid is working. Too high may mean an underactive thyroid; too low may mean an overactive one.
U
V
Vitamin D
A fat-soluble vitamin (technically a hormone) that supports bone health, immune function, mood, and muscle strength. Deficiency is extremely common, especially in women.
VO2 Max
The maximum amount of oxygen your body can use during intense exercise. It's one of the best markers of heart and lung fitness, and a strong predictor of longevity.
W
Waist-to-Hip Ratio
Your waist measurement divided by your hip measurement. It shows where your body stores fat — carrying more fat around your waist is linked to higher health risks.