# Interval Flow vs Muscles

The clearest difference is device support: Interval Flow at 3 against Muscles's 1. Interval Flow also leads on iOS requirement (15.6 vs 17.0). On price, update cadence, ads and in-app purchases there is nothing between them.

Both are free to download. Interval Flow sells 1 one-off in-app purchase and Muscles sells 1 one-off in-app purchase. Whichever you choose, the download price is not the number that matters.

Interval Flow ships an update every 2 weeks, Muscles fortnightly. The most recent releases landed on September 8, 2026 and June 1, 2026 respectively.

## The numbers

| Metric | Interval Flow | Muscles |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[5.0 (3 ratings)](https://appshunter.io/ios/app/muscles-workout-tracker/id6476836905/reviews)** |
| Number of ratings | — | **3** |
| Positive reviews | — | 100.0% of reviews |
| In-app purchases | Yes | Yes |
| Ads | No | No |
| Update frequency | **Every 2 weeks** | Fortnightly |
| Monetization | — | Free with in-app purchases |
| Size | 8 MB | 2 MB |
| Requires iOS | **15.6** | 17.0 |
| Devices | **iPhone, iPod, Apple Watch** | iPhone |
| Age rating | 4+ | 4+ |
| Developer | [Tegyaan](https://appshunter.io/developer/1711584632) | [Nathan Armstrong](https://appshunter.io/developer/982863187) |

## What reviewers say

### Interval Flow

[App page](https://appshunter.io/ios/app/interval-flow/id6469113776)

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Multiple Programs | $3.99 | one-time |


### Muscles

[App page](https://appshunter.io/ios/app/muscles-workout-tracker/id6476836905)

This app offers a streamlined and intuitive way to log your exercise sessions. Easily track your progress with visual analytics and motivational graphs. Its beautiful interface makes fitness tracking enjoyable for all levels.

**Highlights:** Effortless workout logging, Customizable exercise tracking, Progress visualization with graphs, Insightful analytics and statistics, Beautiful and minimalist interface, Dashboard widgets for quick insights

**Features:** macOS Compatibility, Family Sharing

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Full Access | $4.99 | one-time |


## Frequently asked questions

### Is Interval Flow free?

Interval Flow is free to download, with in-app purchases available.

### Is Muscles free?

Muscles is free to download, with in-app purchases available.

### Do Interval Flow or Muscles have ads?

Neither Interval Flow nor Muscles shows ads.

### Which is updated more often, Interval Flow or Muscles?

Interval Flow ships an update every 2 weeks, and Muscles fortnightly. Most recently, Interval Flow was updated on September 8, 2026 and Muscles on June 1, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*