Corpus Notes
Better check-ins start with better questions.
Practical guides to body composition, progress photos, and recovery—sourced, qualified, and written without the hype.
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Progress tracking
Why Your Weight Changes Before Your Body Does
Daily weight includes water, food, glycogen, and more. Learn how to read the trend without mistaking a normal fluctuation for lost progress.
One useful question
What can this number actually tell you?
Body composition
The Navy Body Fat Formula: How It Works and How Accurate It Is
The Navy formula estimates body fat from height, neck, waist and hips. Studies against DEXA found it reads about 4 to 6 points low and can miss weeks of fat loss.
Training & recovery
Resting Heart Rate by Age: A Chart Built From Real Data
A resting heart rate by age chart from US survey and wearable data: kids fall from 129 to 78 bpm, adults average 65–72 bpm, and women run a few beats higher.
Progress tracking
Spren App vs. Corpus (2026): Cost, Accuracy Claims and What You Get
What the Spren app costs on the US App Store, what its accuracy claims rest on, and how it compares with Corpus for weekly body-fat tracking. Disclosed comparison.
Body composition
DEXA Scan Alternatives You Can Use at Home
The DEXA scan alternatives worth using are the ones you can repeat: smart scales, calipers, tape and photo apps. What studies show each gets right and wrong.
Body composition
Are Smart Scales Accurate for Body Fat?
Smart scales weigh you accurately but estimate body fat poorly. What studies comparing them with DEXA found, why hydration skews the number, and how to use one for a real trend.
Progress tracking
The Best Ways and Apps to Track Body Composition in 2026
DEXA, smart scales, calipers, tape-measure equations, and photo-based apps like Corpus, Bodilab, and Spren — what each measures, what the evidence says, and which fits your goal. Written by the maker of Corpus, with that bias disclosed.
Body composition
Body Fat Percentage Chart for Men and Women (by Age)
Healthy body fat percentage ranges for men and women by age, from the study most charts are built on — plus what each range tends to look like, when abs show, and why charts disagree.
Progress tracking
Body Recomposition: How to Lose Fat and Build Muscle at the Same Time
Body recomposition means losing fat and gaining muscle at once. What the research says about who can do it, the training and nutrition that drive it, how long it takes, and how to tell it's working.
Body composition
Cutting vs. Bulking vs. Recomp: How to Choose
Should you cut, bulk, or recomp? The evidence-based rates for each phase, a simple way to choose based on body fat and training experience, and how to track whether it's working.
Progress tracking
How to Know If You're Gaining Muscle or Fat
The scale can't tell muscle from fat. Here are the signals that can — waist vs. weight, strength, photos, and composition trends — and why the first few weeks of training can fool you.
Body composition
How Much Muscle Can You Gain Naturally?
An honest answer to 'how much muscle can I gain in a month?' — what the research can and can't say, the FFMI data behind 'natural limits,' realistic rates of weight gain, and how to see slow progress.
Progress tracking
Losing Inches but Not Weight: What's Actually Happening
Your waist is shrinking but the scale won't move. The usual explanations — recomposition, water, glycogen, and weekly weight rhythms — and how to tell which one applies to you.
Body composition
Skinny Fat: What It Means and How to Fix It
Skinny fat means a normal weight with relatively high body fat and little muscle. What the research calls it, why BMI misses it, how to measure it, and what usually works.
Training & recovery
How to Know When It's Time to Deload
Deloads exist to prevent overreaching before it happens, not to fix it after it does. Here's how to recognize the signs and what a useful deload week actually looks like.
Training & recovery
HRV on Apple Watch: What the Number Means (and Doesn't)
How Apple Watch measures HRV, how accurate it actually is compared to lab equipment, and what to do with the number once you have it.
Progress tracking
How Often Should You Actually Measure Body Composition?
Daily, weekly, or monthly? Different signals, weight, photos, body fat trend, FFMI, are useful at different frequencies. Here's a practical cadence for each.
Progress tracking
How to Take Progress Photos That Are Actually Comparable
Progress photos only work if two shots are actually comparable. Here's the practical setup, lighting, distance, pose, and timing, that removes the variables that aren't your actual progress.
Body composition
DEXA vs. Calipers vs. BIA vs. Photo: How Accurate Is Each Body Fat Method?
A straight comparison of the four common ways to estimate body fat percentage, DEXA, skinfold calipers, bioelectrical impedance, and photo-based estimates, and what each one actually gets wrong.
Body composition
What Body Fat Percentage Actually Looks Like
Body fat percentage numbers mean little without a visual reference. Here's what the common ranges actually tend to look like, and why the same number can look different on different people.
Training & recovery
HRV, Sleep, and Training Readiness for Lifters
HRV can add useful recovery context, but it is not a green or red light by itself. Learn how to read a personal baseline alongside sleep and training load.
Body composition
FFMI, Explained Without the Bro Science
Understand Fat-Free Mass Index, how to calculate it, why body-fat estimates affect it, and how to use an FFMI trend with appropriate caution.