Author
Felipe Passos
Founder of Corpus
Felipe Passos is the founder of Corpus and the person who writes and maintains the guides on this site.
He has been strength training for about ten years — as a serious, long-term hobby rather than a profession. Outside the gym he spends as much time as he can outdoors: hiking, staying active, and treating fitness as a way of living rather than a phase.
He builds Corpus around the questions that long-term training keeps raising: what actually changed, what a number can and cannot tell you, and what is worth doing next.
Transparency
Felipe is not a physician, dietitian, or certified coach. His guides are built on published research — every article lists the studies it relies on — and they explain measurement and interpretation, not diagnosis, treatment, or individual medical advice.
How articles are researched and reviewed →Writes about
- Strength training
- Body composition tracking
- Progress photos
- Fat-Free Mass Index (FFMI)
- Recovery metrics (HRV, sleep, resting heart rate)
Guides by Felipe
- 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.
- 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.
- 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.
- 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.
- 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.
- 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 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
Stop guessing. Start tracking it for real.
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