The Corpus blog
Progress tracking
Tracking physique progress well is less about which tool you use and more about consistency: the same weigh-in routine, the same photo conditions, the same review cadence. Get those right and even a simple method becomes useful. Get them wrong and even a sophisticated one produces noise.
The biggest failure mode is reacting to single data points, one weigh-in, one photo, one score, instead of trends. Daily weight moves several pounds from water and food alone; a single photo can look different from lighting or pose changes that have nothing to do with your actual physique. The guides here are about building a measurement habit that filters that noise out instead of amplifying it.
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.
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 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.
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.
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.
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.
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.
Common questions on this topic
How much does the Spren app cost?
Spren is free to download with in-app purchases. Its US App Store listing, checked in October 2026, shows Annual $69.99, Annual $119.99, Monthly $14.99, Monthly $19.99 and Quarterly $59.99, plus Scan Essentials at $10.49 and $38.99.
Full guide: Spren App vs. Corpus (2026): Cost, Accuracy Claims and What You Get →Is the Spren app accurate?
Spren says its results are comparable to DEXA scans and that its imaging algorithm has been validated by independent peer-reviewed studies. The image studies it lists were done in young adults and fed a photo-based body volume estimate into lab body-composition models, and a 2026 review found photo apps less accurate for individuals than for groups.
Full guide: Spren App vs. Corpus (2026): Cost, Accuracy Claims and What You Get →What is the most accurate way to track body composition?
DEXA and laboratory multi-compartment methods are the most accurate for a single reading, but they're impractical to repeat often. For week-to-week tracking, a method you can repeat under identical conditions — a photo-based app, a smart scale, or a tape or skinfold equation — is more useful, as long as you compare it only with itself.
Full guide: The Best Ways and Apps to Track Body Composition in 2026 →Is there an app that measures body fat from a photo?
Yes — several apps estimate body fat from photos, including Corpus, Bodilab, and Spren. A 2026 research review found such apps generally accurate at the group level but less accurate for individuals and at higher body fat, so treat any app's number as an estimate and focus on the trend.
Full guide: The Best Ways and Apps to Track Body Composition in 2026 →Who can do body recomposition?
More people than the old 'beginners only' rule suggests. Research reviews describe it in untrained and trained people, older adults, people with overweight, and athletes including bodybuilders. It is usually faster for beginners and people returning after a break, and slower for lean, experienced lifters.
Full guide: Body Recomposition: How to Lose Fat and Build Muscle at the Same Time →Should I eat at maintenance or in a deficit to recomp?
Both can work. Many people recomp at roughly maintenance calories or a small deficit. If you are in a deficit, slower weight loss protects lean mass better — in one study, athletes losing 0.7% of body weight per week gained lean mass while those losing 1.4% did not.
Full guide: Body Recomposition: How to Lose Fat and Build Muscle at the Same Time →How do I know if weight gain is muscle or fat?
Compare your weekly average weight with your waist measurement and your strength. Weight rising with a stable waist and climbing lifts points mostly to lean tissue; a waist rising in step with the scale points to more fat. Comparable photos and a consistent composition estimate add confirmation.
Full guide: How to Know If You're Gaining Muscle or Fat →How fast should I gain weight to build muscle without much fat?
A 2019 review recommends a target of about 0.25–0.5% of body weight per week for novice and intermediate lifters, with more advanced lifters going slower. Faster gains mostly add fat.
Full guide: How to Know If You're Gaining Muscle or Fat →Glossary terms