A planning assumption, not a measurement. These hours are guide values the app plans with. How fast you recover depends on training intensity, sleep, nutrition and training experience. Updated 27 September 2026.
Recovery Check: Are Your Muscles Recovered? Calculate in Real Time
You trained yesterday and wonder: can I train chest again today? The answer depends on when you trained, which muscle group, how old you are and how hard the session was. The free MUSCLE TECHNICS Recovery Check works it out in seconds, with guide values we disclose below.
And because almost every recovery rule in fitness goes back to the same small study, we take a closer look at it: what it shows and what it does not.
What the Recovery Check does
You enter when you last trained and which muscle groups. The check then calculates in real time which of three phases each trained muscle is in:
Phase 1: Recovering (blue). The muscle is still repairing. Training it hard now means starting fatigued and getting fewer good reps. The check shows exactly how many hours remain.
Phase 2: Ready (green). The muscle has recovered and is ready for the next stimulus. Now is a good time for your next session. The check shows how long the window remains open.
Phase 3: Stimulus faded (red). The growth signal from your last session is over. Your progress stays, but the muscle needs the next stimulus to keep growing. Up to about 2 weeks off, studies in trained lifters show no measurable loss of maximal strength. After that, strength can slowly decline.
The 48-hour window: what the study really shows
"Train again after 48 hours", "after 72 hours the stimulus is gone", "supercompensation": these rules appear in countless training plans. Almost all of them go back to a few measurements from the 1990s. The best known is a 1995 study by MacDougall and colleagues.
What was measured
Six young men trained one arm with 12 heavy sets of biceps exercises; the other arm stayed untrained as a control. The researchers measured how fast the biceps built new protein (muscle protein synthesis). Earlier measurements had shown that it rises sharply after training, to about double after 24 hours. In this study, after about 36 hours it was only 14% above the untrained arm, a difference that was not statistically significant.
A second study (Phillips 1997, eight untrained women and men, measured fasted) still found synthesis 34% higher after 48 hours. But breakdown rose as well, so in the fasted state the balance of building and breakdown stayed negative the whole time.
These numbers became the familiar rule: the growth stimulus lasts one to two days, then the next one has to follow.
Why the study shows less than people think
Very small and very narrow. Six men, one muscle, one exercise, a single session. It says nothing about whether legs, back or women respond the same way.
Protein synthesis is not muscle growth. Only building was measured, not breakdown. Muscle only grows if, over weeks, more is built than broken down.
After the first sessions, most of it goes into repair. Damas and colleagues (2016) followed this over ten weeks: in week one the rise in synthesis was largest but was not related to later growth. It coincided with the most muscle damage. Only from week three on was it related to growth.
Trained people respond differently. In the same study the response after three and after ten weeks of training was clearly smaller than the first time. Measurements in beginners cannot simply be transferred to trained lifters.
And "supercompensation"?
The word comes from research on carbohydrate stores. In 1966 Bergström and Hultman showed that the glycogen stores of an exercised leg can refill above their starting level. Later this picture was transferred to strength and muscle growth: after training, performance drops, then briefly rises above the old level, and that is exactly when the next stimulus should come. For muscle growth this window has never been measured that way. It is a vivid model, not a measurement.
What is well supported instead
Frequency is secondary, volume matters. An analysis of 25 studies (Schoenfeld 2019) found that with the same number of hard sets per week, it hardly matters for muscle growth whether you train a muscle once or three times a week. There is no narrow window you have to hit.
Breaks cost less than you think. In one study, one group trained for 24 weeks straight while the other took three weeks off after every six weeks. In the end both groups had gained the same amount of muscle and strength (Ogasawara 2013, 14 young men, bench press).
What this means for you
The hours in the Recovery Check are guide values for planning, not a stopwatch. A day earlier or later changes little about your progress.
What matters is enough hard sets per week, progression over time and enough recovery in between.
"Stimulus faded" does not mean anything is lost. It only means: if you want to keep growing, it is time for the next session.
The guide values in the check
Each muscle group gets its own recovery time. These are guide values from training practice, not measurements from a study:
Muscle group
Recovery time
Abs
~30 hours
Arms (biceps/triceps)
~48 hours
Chest
~56 hours
Shoulders
~56 hours
Back
~60 hours
Legs
~60 hours
Age adjustment
From age 30, the check plans more time. It multiplies the guide values: under 30 ×1.0, 30–39 ×1.1, 40 and over ×1.2. In the app, intermediate and advanced lifters get ×1.1 from 40. In the check, a 45-year-old's chest therefore needs 67 instead of 56 hours (62 in the app with training experience).
How the check works
Step 1: Enter your age. This determines your individual recovery times.
Step 2: Select the day of your last workout from the past 7 days (retrospective: today is on the right). Then the approximate time and which muscle groups you trained.
Step 3: The check instantly calculates the real-time status of each muscle group, with a color-coded bar, phase indicator and concrete time values.
What the check can NOT do, but the app can
The Recovery Check shows the recovery status for a single workout. That's useful, but it's a snapshot. What the MUSCLE TECHNICS app does on top:
Automatic recovery tracking: The app tracks every workout and calculates recovery for every exercise automatically, including fractional volume for compound exercises.
Plateau detection: The app calculates your e1RM after every set and detects stagnation after 4 weeks without a new best automatically.
Deload on fatigue: After a longer stretch of training, the coach plans a deload session when your recovery check-in shows high fatigue. There is no fixed block of 4-6 weeks.
AI coach: An LLM-based coach that analyzes your complete training history and creates a new optimal plan every day, with explanations.
The Recovery Check shows you if your muscle is ready. MUSCLE TECHNICS tells you when, what and how much to train.
Yes. No registration, no login, no hidden costs. The check runs entirely in your browser; no data is sent to a server.
Where do the recovery times come from?
They are guide values from training practice, not measurements from a study: abs 30 hours, arms 48, chest and shoulders 56, back and legs 60. From age 30 the check plans more time: +10% from 30 and +20% from 40.
Is it true that muscle growth is over after 48 hours?
Not in that general form. The well-known study (MacDougall 1995) measured only the biceps of six men, and only protein building, not muscle growth. What is well supported: with the same weekly volume, how often per week you train a muscle hardly matters for growth.
What is supercompensation, and does the model hold up?
The model says: after training, performance drops, then briefly rises above the old level, and that is when the next stimulus should come. The word comes from research on carbohydrate stores. For muscle growth this window has never been measured that way. It is a vivid picture, not a measurement.
What do the three phases mean?
Blue (recovering): the muscle is still repairing; a hard session now starts fatigued. Green (ready): the muscle has recovered, a good time for the next session. Red (stimulus faded): the growth impulse of the last session is over. Your progress stays; for further growth the muscle needs the next stimulus.
Can I save or share the result?
Yes. "Save PDF" downloads the report as a PDF, and the share button sends it as a link.
What is the difference between the Recovery Check and the app?
The Recovery Check shows the status after a single session. The MUSCLE TECHNICS app works with every session you log, detects plateaus, plans a lighter session when you have trained for a longer stretch and report high fatigue, and creates a training plan every day.
Sources
MacDougall JD et al. (1995): The time course for elevated muscle protein synthesis following heavy resistance exercise. Can J Appl Physiol 20(4):480–486. doi:10.1139/h95-038
Phillips SM et al. (1997): Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am J Physiol 273(1):E99–E107. doi:10.1152/ajpendo.1997.273.1.E99
Damas F et al. (2016): Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage. J Physiol 594(18):5209–5222. doi:10.1113/JP272472
Schoenfeld BJ, Grgic J, Krieger J (2019): How many times per week should a muscle be trained to maximize muscle hypertrophy? J Sports Sci 37(11):1286–1295. doi:10.1080/02640414.2018.1555906
Ogasawara R et al. (2013): Comparison of muscle hypertrophy following 6-month of continuous and periodic strength training. Eur J Appl Physiol 113(4):975–985. doi:10.1007/s00421-012-2511-9
Bergström J, Hultman E (1966): Muscle glycogen synthesis after exercise: an enhancing factor localized to the muscle cells in man. Nature 210:309–310. doi:10.1038/210309a0