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Aisha Karim

Articles by Aisha Karim

Fitness & running writer · View profile

· 13 min read

Gear Inches, Development, and Why Cyclists Argue About Ratios

50/11 means nothing until you attach a wheel. Gear inches and metres of development, derived and converted, a full table for a real 12-speed drivetrain, and why the gear step between two sprockets decides whether you can hold a cadence.

· 13 min read

Expected Goals: What xG Actually Measures

xG is the fitted probability that a shot with a given set of features becomes a goal — a model output, not an observation. A worked match, the binomial arithmetic that says one game is far too few shots, and the limits nobody quotes.

· 15 min read

Climbing Grade Conversions Are Not Conversions

French, YDS, UIAA, V-scale and Font are ordinal scales with no underlying unit. A conversion table is a negotiated alignment between climbing communities — and published tables disagree by half a grade at the top and by four letter-grades at the bottom of the boulder scales.

· 3 min read

How to Calculate Your Running Pace

Running pace is time per kilometre or mile. Here's how to work it out from any run, convert between units, and use it to pace a race without blowing up.

· 10 min read

ERA, FIP and WHIP: Three Answers to One Question

ERA measures what happened, FIP measures only what the pitcher controls without his fielders, WHIP measures traffic allowed. Two pitchers can swap places entirely between them — and the gap between ERA and FIP is a forecast, not a verdict.

· 10 min read

OPS Is a Flawed Sum, and Still the Most Useful Number on the Card

OPS adds two fractions with different denominators, which as arithmetic is indefensible. It survives because it tracks run scoring far better than batting average and costs nothing to compute — but it underpays on-base ability, and OPS+ does not fix that.

· 13 min read

Vertical Jump to Power: What the Conversion Assumes

Turning jump height into take-off velocity is exact physics. Turning it into watts is a regression fitted on somebody else's athletes — and the three common formulas disagree by thousands of watts on the same jump.

· 13 min read

FFMI: The Number BMI Cannot Give You

BMI weighs you and divides by your height squared. It cannot tell muscle from fat, which is why lean athletes get classed overweight. FFMI removes the fat first — and inherits every error in the body-fat estimate it is built on.

· 14 min read

One-Rep Max Formulas Disagree, and the Disagreement Is the Point

Epley, Brzycki, Lombardi, O'Conner and Wathan are five curves through the same data. They agree within a few pounds at low reps and disagree by a quarter at fifteen — which is exactly how you know when an estimate is worth having.

· 12 min read

SWOLF: What It Measures, and What It Rewards

SWOLF adds seconds to strokes, which is dimensionally indefensible and useful anyway. The catch is what it rewards: it prices one stroke at exactly one second, so it can improve while you get slower — and it is not comparable between pools of different lengths.

· 12 min read

Cycling Speed Is Mostly a Fight With Air

Rolling resistance grows with speed, air resistance grows with its square, and power grows with its cube. Work the equation and the crossover falls at 10 mph — after which almost everything you pay for is air, and a headwind costs more than the same tailwind returns.

· 12 min read

Hiking Pace: Naismith's Rule and the Corrections It Needs

Naismith's 1892 rule times a route in two lines of arithmetic. It also ignores descent completely and assumes a fit walker with no pack. Here is the rule, Langmuir's fix, and Tobler's continuous alternative — whose fastest speed is on a downhill, not on the flat.

· 12 min read

Maximal Aerobic Speed: The One Number That Sets Every Training Pace

Maximal aerobic speed is the slowest speed at which you reach your VO2max. Because it is a speed and not a heart rate, every training zone becomes a percentage of something you can measure on a track — and the whole week falls out of one test.

· 2 min read

How Many Calories Does Running Burn?

Running burns roughly your body weight in calories per kilometre. Here's the simple rule, what changes it, and how running compares to walking.

· 2 min read

What Is VO2 Max?

VO2 max is the most oxygen your body can use during hard exercise — a benchmark of aerobic fitness. Here's what it means, typical values, and how to raise it.

· 3 min read

How to Estimate Your One-Rep Max (1RM)

Your one-rep max is the most you can lift once. Here's how to estimate it safely from a lighter set, how accurate it is, and how to train with it.

· 2 min read

How to Pace a 5K

Divide your goal time by 5 to get the pace to hold, then run even splits. Here's how to find your target pace, train for it, and race it well.

· 2 min read

How Many Steps to Burn Calories?

Walking burns roughly 0.04 calories a step. Here's what 10,000 steps really burns, what changes the number, and whether 10,000 is a magic figure.