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Mass in Motion is a hybrid athlete training app built for people who both run and lift. It writes your weekly training plan, adapts the plan as your fitness and recovery change, and makes sure your lifting and running sessions don't sabotage each other.

The app handles running pace zones, strength block progression, interference management (making sure your leg-intensive sessions aren't stacked on top of each other), and recovery scoring — all automatically.

Mass in Motion is currently in closed beta on TestFlight (iOS). Android support is planned. Join the waitlist at massinmotionapp.com and you'll get an email when beta slots open, along with founding-member pricing before public launch.

Submit your email on the waitlist. Beta slots are rolling — we open them as development milestones hit. Waitlist members are invited first, in order of signup.

You can also follow along and ask questions on Reddit (u/massinmotionapp) — we post sprint updates there regularly.

The app is built in Flutter and targets iOS and Android. The active beta is iOS via TestFlight. Android and a web companion dashboard are on the roadmap.

Pricing details will be confirmed before public launch. Beta testers get access to a founding-member rate that locks in before general availability. The plan is to offer a free tier with core logging and a paid tier for the adaptive algorithm, pace zone coaching, and full wearable sync.

Pace zones are derived from your recent race performances or time-trial results — not generic heart rate bands. The algorithm back-calculates your aerobic threshold and VO2max-equivalent pace from your best recent effort, then sets 5 training zones around those anchors.

As your fitness improves and you log faster times, your zones automatically shift up. You never have to manually re-enter a threshold pace. Read more in the pace zones guide.

The app programs across the full spectrum of structured running:

• Easy / Zone 2 — aerobic base, recovery runs
• Tempo & Threshold — lactate threshold development
• Interval / VO2max — high-intensity repeats at 5K–3K effort
• Long runs — progressive or steady-state, scaled to your goal race distance
• Race-pace work — goal-pace segments tuned to your target event

The weekly mix is adjusted based on your training phase, recovery score, and time budget.

Yes. You can set a target race distance and date and the algorithm will periodize your running block to peak at that event — building base, adding specific quality work, then tapering in the final weeks.

Yes. Mass in Motion supports Strava OAuth2 integration. When connected, completed runs sync automatically into your workout log so you don't need to log the same run twice. The app reads your GPS, pace, and distance data to keep your pace zones and ACWR load score current.

ACWR (Acute-to-Chronic Workload Ratio) compares your recent weekly load against your rolling 4-week training load. When ACWR spikes above ~1.5, injury risk rises sharply. Mass in Motion tracks ACWR separately for running and lifting and gates session recommendations when your ratio is in the danger zone.

See the full explainer: ACWR: The Science of Not Overtraining.

Mass in Motion supports four distinct lifting program styles, each built around your goals and available training time:

• High-intensity low-volume hypertrophy — fewer total sets at very high effort, close to failure. Efficient for athletes with tight time budgets who still want muscle growth stimulus.
• High-volume hypertrophy — more sets per muscle group per week to maximize hypertrophy stimulus, using moderate-to-high RIR targets across a larger exercise selection.
• Traditional strength training — lower-rep, heavier work focused on building peak strength in core movement patterns with structured progressive overload.
• Conjugate-style training — rotating maximal-effort and dynamic-effort days with exercise variation to manage fatigue and target weaknesses across the training cycle.

Mass in Motion uses RIR (Reps in Reserve) — not RPE — for autoregulation. After each set you log how many reps you could have done before failure. The algorithm uses that number to project your performance on the next session and adjust load, sets, or reps accordingly.

RIR is more intuitive than RPE for most athletes and gives the algorithm a clearer signal of proximity to failure without requiring you to estimate exertion on a 1–10 scale.

Yes — sessions are designed to reach ~85–90% of your stated time budget. If the primary exercises don't fill the window, the algorithm adds accessory work or adjusts volume rather than leaving you with dead time. You tell the app how long you have; it fills the session intelligently.

The app uses interference management to sequence lifting and running sessions so they don't compound fatigue. The main rules:

• Heavy lower-body lifting is never placed the day before a hard run
• High-intensity running is not scheduled immediately after heavy squats or deadlifts
• Upper-body or accessory days can float adjacent to easy runs without penalty

The algorithm re-sequences sessions dynamically when your schedule changes or recovery score drops.

The Recovery Score is a 0–100 daily readiness number derived from HRV (heart rate variability), resting heart rate, and sleep duration. A score above 70 signals you're ready for a hard session. Below 50 triggers the algorithm to recommend an easier or deload session instead.

The score uses an exponentially weighted rolling baseline so one bad night doesn't tank your number long-term. Read the full methodology: HRV & Your Daily Recovery Score.

Mass in Motion works with:

• Apple Health — the primary sync layer for iOS. Any device that writes to Apple HealthKit (Apple Watch, Garmin, Polar, Wahoo, etc.) feeds into the app automatically.
• WHOOP — direct OAuth2 integration for HRV, recovery, and strain data from WHOOP bands.
• Strava — OAuth2 integration for run data, GPS, and pace history.

If your wearable writes to Apple Health, it's already compatible on iOS without a separate integration.

Yes. Wearable data improves the accuracy of the Recovery Score and ACWR tracking, but the app works without one. You can manually log workouts, enter sleep duration, and the algorithm will still adapt your program — it just won't have HRV data to refine the readiness signal.

Heart rate variability (HRV) is the variation in time between consecutive heartbeats. Higher HRV generally indicates your autonomic nervous system is recovered and ready for stress. Lower HRV signals accumulated fatigue or incomplete recovery.

Mass in Motion uses HRV as one of three inputs (alongside resting HR and sleep) to compute your daily Recovery Score. Because HRV is highly individual, the app builds a personal baseline over your first 2–4 weeks rather than comparing you to population averages.

Deloads are triggered automatically when your recovery score or ACWR indicates accumulated fatigue — you don't need to schedule them manually. The algorithm reduces volume by roughly 40% while maintaining session frequency so you don't lose the habit. If your metrics are fine, the app won't waste a week on an unnecessary deload.

The algorithm combines three real-time signals to generate each session:

• Recovery Score — determines session intensity ceiling
• ACWR — gates load increases to keep injury risk low
• Performance feedback — RIR logs tell the algorithm how close you are to failure and adjust next session's targets

Every session is written fresh based on the current state of these signals. If you had a rough night, your next session is softer. If you're crushing your sets with plenty of RIR left, the algorithm increases load. No static spreadsheet — the plan changes as you do.

The HRV baseline stabilizes after roughly 2–4 weeks of daily readings. Pace zones lock in after your first time trial or recent race result. Strength baselines update after 2–3 completed sessions per exercise. From that point the algorithm has enough signal to adapt meaningfully — early sessions use conservative defaults.

Yes. The algorithm's session recommendations are a starting point, not a mandate. You can adjust individual sets, swap exercises, defer a session, or mark a workout as complete regardless of what was planned. The algorithm incorporates your actual logged data — not just its own prescriptions — when calculating the next session.

Concurrent training (running and lifting in the same program) creates an interference effect where cardio adaptations can blunt strength gains and vice versa — especially when sessions are scheduled poorly. Mass in Motion minimizes interference by:

• Separating high-intensity modalities by at least 6–8 hours when possible
• Sequencing lifting before running on same-day doubles (not after)
• Keeping heavy lower-body work away from hard run days
• Tracking cumulative fatigue across both modalities in a single load score

Read more: Hybrid Athlete Training: Run and Lift Without Compromise.

You can request account deletion at any time from Settings → Account → Delete Account inside the app, or by submitting the form on the account deletion page. All personal data is permanently removed within 30 days per our Privacy Policy.

Mass in Motion collects the data you provide (email, workout logs, settings) and health data from connected wearables (HRV, resting HR, sleep, run pace). We do not sell your data to third parties. Full details are in the Privacy Policy and Consumer Health Privacy Policy.

Yes. Your health data is secured with per-user access controls — your records are only accessible to your authenticated account. Data in transit is encrypted via HTTPS. We collect only the biometric signals the algorithm needs to function and do not build secondary profiles or share raw health data externally.

Data export is on the roadmap. In the current beta, you can view your full workout history inside the app. If you need a data export urgently (e.g., before account deletion), email brandon@massinmotionapp.com and we'll get it to you manually.

Email brandon@massinmotionapp.com with a short description of what happened, what you expected, and your device / iOS version. Screenshots or screen recordings are always helpful. Bug reports from beta testers directly shape what gets fixed in the next sprint.