Top Apps to Track Lean Muscle Mass
App guide
Ranked & compared
RENPHO Health (free app, smart scale required) is the most accessible at-home lean-mass tracker; MacroFactor is the best app for the protein-intake side of muscle preservation; Strong logs the resistance training that makes preservation possible — used together, these three apps cover the full lean-mass protection stack for GLP-1 users.
Lean mass loss is the most clinically significant body-composition risk of GLP-1 therapy, with trial data showing lean tissue accounts for roughly one-third to nearly half of all weight lost. Tracking it requires a three-part approach: measuring body composition trends, hitting protein targets, and logging resistance training. This guide covers the best apps for each piece of that stack, how to interpret their data together, and what warning signs warrant a conversation with your prescriber.
This is general nutrition and wellness information, not medical advice. If you're on a weight-loss medication or managing a health condition, confirm specifics with your clinician.
What you're actually tracking
Lean muscle mass tracking is the single most GLP-1-relevant tracking topic in this category. A Circulation review of registration trials found that lean mass made up 45.5% of weight lost in STEP 1 (semaglutide) and 34.3% of weight lost in SURMOUNT-1 (tirzepatide). These figures — drawn from body-composition sub-analyses of randomized trials — mean that roughly one-third to nearly half of all weight lost on these drugs includes lean tissue, not just fat. Tracking lean mass, protein intake, and resistance training together is the evidence-informed response to this risk.
How we evaluated them
Evaluated on: ability to measure or track lean mass directly; protein-intake tracking for muscle preservation; resistance-training logging to provide the exercise stimulus; data accuracy; price transparency; and specific clinical relevance to lean-mass loss during GLP-1 therapy.
The apps, side by side
No single app wins for everyone — each card calls out who it's genuinely best for, so you can pick on fit, not hype.
RENPHO Health
Free app (RENPHO smart scale sold separately)iOS / AndroidBest for: Home lean-mass and muscle tracking via smart BIA scale
- Estimates muscle mass, body water, and BMR
- Syncs Apple Health
- Tracks trend over time
- BIA estimates fluctuate with hydration and time of day
MacroFactor
$11.99/mo / $71.99/yr (no free tier; 7-day trial)iOS / AndroidBest for: Protein-target enforcement to protect lean mass nutritionally
- Adaptive protein/macro targets updated weekly from actual intake and weight data
- Verified food database
- No free tier; subscription only
Strong
Free (3 routines) / Premium $4.99/mo or $29.99/yriOS / AndroidBest for: Resistance-training logging to build and retain lean muscle
- Fast set/rep logging
- Plate calculator and 1RM estimates
- Workout history and PR tracking
- Unlimited routines and advanced analytics are Premium-only
The Lean Mass Problem With GLP-1 Drugs: What the Trial Data Actually Says
When the scale drops on semaglutide or tirzepatide, not all of that weight is fat. A Circulation review of the STEP 1 and SURMOUNT-1 body-composition sub-analyses found that lean mass accounted for 45.5% and 34.3% of total weight lost, respectively. That is not a rounding error — it is a central finding that shapes how anyone on these medications should approach nutrition and exercise.
Lean mass in these trials is measured by DEXA and includes skeletal muscle, but also body water, organ tissue, and connective tissue. UC Davis Health exercise physiologists have pointed out that the proportion that is actual contractile muscle is lower than the headline number suggests. Still, even a conservative estimate puts muscle loss in the range of 20–30% of total weight lost, which is clinically meaningful over a 12-to-18-month treatment course.
The mechanism is straightforward: rapid weight loss, particularly when calorie intake drops sharply, creates a catabolic environment. The body breaks down muscle protein for energy unless it receives a strong signal to do otherwise. That signal comes from two places — adequate dietary protein and mechanical tension from resistance training. Without both, the muscle fraction of weight loss rises. The 2025 multi-society Advisory from ACLM, ASN, OMA, and The Obesity Society formalized this by proposing a protein target of 1.2–1.6 grams per kilogram of body weight per day during active weight reduction, paired with resistance exercise. This is the clinical foundation that any tracking app stack should be built on.
Bottom line
A Circulation review found lean mass was 45.5% of weight lost in STEP 1 (semaglutide) and 34.3% in SURMOUNT-1 (tirzepatide) — this is the scientific basis for prioritizing protein intake and resistance training on GLP-1, and it's what an app stack should be built around.
How to Track Lean Mass at Home: BIA Scales, DEXA, and What Apps Can Do
The most practical at-home method for tracking lean mass is bioelectrical impedance analysis, or BIA — the technology inside smart scales like those from RENPHO. BIA sends a weak electrical current through the body and estimates lean mass based on how quickly that current travels. Muscle, which is roughly 75% water, conducts electricity well. Fat does not. The RENPHO Health app takes that raw impedance data from the scale and converts it into estimates of muscle mass, lean body mass, body water, and basal metabolic rate.
The catch is that BIA is highly sensitive to hydration status. If you weigh yourself dehydrated in the morning, your lean mass reading will be lower than if you weigh yourself well-hydrated in the evening — even though your actual muscle tissue has not changed. This is not a flaw unique to RENPHO; it is a limitation of all consumer BIA devices. The fix is consistency: weigh yourself at the same time each day, ideally first thing in the morning after using the bathroom and before eating or drinking. Track the trend line over weeks and months, not the day-to-day number.
DEXA scans remain the consumer gold standard for body composition. A DEXA scan costs roughly $50–150 out of pocket and provides a three-compartment model — bone, fat, and lean tissue — with far greater precision than BIA. For GLP-1 users who want a definitive answer on muscle preservation, getting a DEXA scan at baseline and then every three to six months is a reasonable strategy. The RENPHO app fills the gap between scans, providing a daily trend that can flag problems early. If the RENPHO lean-mass trend is flat or rising, muscle is likely being preserved. If it is dropping steadily across four or more weeks, that is worth investigating with a DEXA or a conversation with your prescriber.
Bottom line
RENPHO Health provides a consistent lean-mass trend rather than an accurate absolute number — weigh at the same time each day (morning, fasted, post-bathroom) to minimize hydration variation and focus on the direction of change, not the exact figure.
The Protein-Side of Lean Mass: MacroFactor and the 1.2–1.6 g/kg Target
Dietary protein provides the amino acid building blocks that muscle tissue needs to repair and maintain itself. During GLP-1-driven weight loss, when total calorie intake drops — often dramatically — hitting a protein floor becomes both harder and more important. The 2025 multi-society Advisory proposed 1.2–1.6 grams of protein per kilogram of body weight per day during active weight reduction. For a 200-pound person, that is roughly 109–145 grams of protein daily. On a reduced-calorie diet, that requires deliberate food choices.
MacroFactor is built specifically for this problem. Unlike static calorie trackers that set a protein goal once and leave it, MacroFactor recalculates your targets every week based on your actual weight change and logged intake. If you lose three pounds in a week, your protein target in grams adjusts downward — but the grams-per-kilogram ratio stays locked in. This matters on GLP-1 because weight can drop faster than on lifestyle-only diets, and a protein target set at 220 pounds will be too high at 200 pounds. MacroFactor's adaptive algorithm keeps the target clinically appropriate without requiring manual recalculation.
The app's food database is verified rather than crowd-sourced, which reduces the risk of inaccurate protein entries. It also tracks your protein-hit rate — the percentage of days you met your target — which is the single most actionable nutrition metric for muscle preservation. If that rate drops below 80%, lean mass is at higher risk. For those who prefer a free alternative, MyFitnessPal's free tier allows setting a custom protein goal in grams. Multiply your body weight in kilograms by 1.2 and set that as your daily minimum. Cronometer's free tier offers similar functionality with a lab-verified database. The trade-off is that neither free app adjusts the target automatically as weight changes.
Bottom line
MacroFactor recalculates your protein target weekly as weight drops — a feature that matters on GLP-1, where target body weight and therefore protein in grams changes faster than on lifestyle-only diets.
The Training Side of Lean Mass: Using Strong to Log Resistance Sessions
Protein without resistance training is like supplying bricks without a construction crew — the raw materials are present, but nothing gets built. Resistance training provides the mechanical tension that signals muscle cells to take up amino acids and synthesize new contractile proteins. The evidence-based minimum for lean-mass preservation during weight loss is two to three sessions per week that cover all major muscle groups: legs, back, chest, shoulders, and arms. Each session does not need to be long — 30 to 45 minutes of compound movements like squats, rows, presses, and deadlifts is sufficient if intensity is adequate.
Strong is built for logging exactly this kind of training. Its free tier supports up to three custom routines, which is enough to cover a push day, a pull day, and a legs day — or a full-body routine done two to three times per week. Logging a set takes two taps: one to select the exercise and one to enter the weight and reps. The app tracks your history on every lift, calculates estimated one-rep maxes, and flags personal records. That PR tracking is the key signal for muscle preservation. If your estimated one-rep max on a compound lift like the barbell squat is stable or rising across four weeks, you have strong evidence that muscle is being maintained — even if the scale and BIA readings are ambiguous.
Declining strength numbers are the earliest accessible warning sign of muscle loss. If your squat or bench press one-rep max estimate drops across four or more consecutive weeks, and your protein-hit rate in MacroFactor is below 80%, the most likely cause is inadequate protein intake. Fix that first. If protein is on target and strength is still declining, the training stimulus itself may be insufficient — consider increasing volume, frequency, or intensity. Bring both the Strong data and the MacroFactor data to your next prescriber or dietitian visit. The combination tells a story that neither app can tell alone.
Bottom line
Stable or improving strength numbers in Strong are the most accessible signal that lean mass is being preserved during GLP-1 weight loss — declining one-rep max estimates across four-plus weeks warrant a protein and training review.
Interpreting 3–6 Months of RENPHO, MacroFactor, and Strong Data Together
Each app in this stack answers a different question. RENPHO asks: is my lean mass trend stable? MacroFactor asks: am I eating enough protein to support that lean mass? Strong asks: is my strength holding, which tells me the muscle is still functional? Reading them together over 90 to 180 days gives you a picture that no single metric can provide.
A winning 90-day picture looks like this: RENPHO lean mass is flat or slightly up, MacroFactor shows protein target hit on more than 80% of days, and Strong shows stable or increasing estimated one-rep maxes on your core lifts. That combination means you are losing fat while preserving muscle — exactly the outcome GLP-1 therapy should aim for. If RENPHO lean mass is dropping but strength is stable, the BIA reading is likely being thrown off by hydration changes or the loss of non-muscle lean tissue like glycogen-bound water. That is less concerning. If both RENPHO lean mass and Strong strength numbers are declining, muscle loss is probable and intervention is needed.
Warning signs to bring to a prescriber or registered dietitian include: a RENPHO lean-mass trend that drops more than 2–3% of total body weight over 12 weeks, a MacroFactor protein-hit rate below 70% for more than two weeks, or declining one-rep max estimates across all major lifts for four or more consecutive weeks. Any one of these is worth a conversation. All three together warrant a DEXA scan to confirm what the home data is suggesting. The scan provides a definitive body-composition measurement that can guide whether protein targets, training volume, or the rate of weight loss itself needs adjustment.
Bottom line
If RENPHO lean mass holds or rises, MacroFactor shows protein target hit more than 80% of days, and Strong shows stable strength — you have strong evidence lean mass is protected. If any one fails, that is the lever to fix first.
What most pages leave out
BIA lean-mass estimates in apps like RENPHO are not clinical-grade measurements. UC Davis Health exercise physiologists have noted that 'lean mass' in GLP-1 registration trials includes fluid, organ tissue, and other non-muscle components — so the 45.5% and 34.3% figures do not mean all that tissue is skeletal muscle. The real skeletal muscle loss is likely lower, but still clinically meaningful. DEXA remains the consumer gold standard for body composition. Competitors often present BIA numbers as precise when they are estimates.
We flag this so you can make an informed choice — not to scare you off.
❓Frequently Asked Questions
RENPHO Health is the best at-home option for tracking lean mass trends via a BIA smart scale. MacroFactor is the best app for enforcing the protein targets that preserve muscle nutritionally. Strong is the best app for logging the resistance training that provides the anabolic stimulus. Used together, these three apps form a complete lean-mass protection stack for GLP-1 users.
Yes, some muscle loss occurs during GLP-1-driven weight loss. A Circulation review of registration trial data found that lean mass made up 45.5% of weight lost in the STEP 1 trial for semaglutide and 34.3% in the SURMOUNT-1 trial for tirzepatide. However, lean mass includes body water and organ tissue, not just skeletal muscle, so the actual muscle-specific loss is lower. Adequate protein intake and resistance training significantly reduce the muscle fraction lost.
A 2025 multi-society Advisory from ACLM, ASN, OMA, and The Obesity Society proposed 1.2 to 1.6 grams of protein per kilogram of body weight per day during active weight reduction. For a 200-pound person, that is roughly 109 to 145 grams daily. MacroFactor adjusts this target automatically as your weight changes, which is helpful on GLP-1 where weight can drop faster than expected.
Yes, RENPHO Health estimates lean mass, muscle mass, body water, and basal metabolic rate using bioelectrical impedance analysis from a RENPHO smart scale. The app is free but requires a RENPHO scale, which is sold separately. Readings fluctuate with hydration, so the trend over time is more useful than any single measurement.
BIA scales provide estimates, not precise measurements. Hydration status, time of day, recent meals, and individual body water distribution all affect the reading. They are useful for tracking trends when used consistently — same time, same conditions — but should not be treated as clinical values. DEXA scans remain the consumer gold standard for accurate body composition measurement.
Evidence-based guidance points to two to three resistance training sessions per week covering all major muscle groups. Each session can be 30 to 45 minutes if intensity is adequate. Logging sessions in an app like Strong helps track consistency and detect strength declines that may signal muscle loss before it becomes visible on a body composition scale.
MyFitnessPal's free tier allows setting a custom protein goal in grams — multiply your body weight in kilograms by 1.2 and set that as your daily minimum. Cronometer's free tier also tracks protein from a lab-verified database. Neither free app adjusts the target automatically as weight changes, so you will need to recalculate manually every few weeks.
The most accessible home signals are declining strength numbers in a workout app like Strong or Hevy, combined with a dropping lean-mass trend in RENPHO. If both are declining across four or more weeks, muscle loss is probable. A DEXA scan provides definitive confirmation and is worth pursuing if the home data is concerning.
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Read moreOn a GLP-1, or thinking about one?
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This content is for general informational purposes only and is not medical or nutritional advice, a diagnosis, or a substitute for professional judgment. It does not account for your health, medications, or goals, and nutrition information changes over time. Always talk with a qualified clinician or dietitian before making significant changes to your diet, supplements, or medications. Curex offers compounded GLP-1 medications through licensed clinicians and does not sell or endorse the food or supplement reviewed on this page.