# HRV4Training vs Nix Solo

The clearest difference is review sentiment: HRV4Training at 61% against Nix Solo's 14%. HRV4Training also leads on chart position (#20 vs unranked) and ratings volume (290 vs 68). Nix Solo's advantage is price (Free vs $9.99) and rating (4.8 vs 3.6). On ads, in-app purchases and iOS requirement there is nothing between them.

Nix Solo is free to download; HRV4Training costs $9.99 up front. Neither carries in-app purchases, so what you see is what you pay.

Nix Solo holds the better App Store score, 4.8 against 3.6. Both are backed by a comparable volume of ratings — 290 and 68 respectively. Written reviews complicate that: 61% of HRV4Training's written reviews are positive against 14% of Nix Solo's, so the app with the better star average is not the one people write more warmly about.

HRV4Training ships an update every 6 weeks, Nix Solo every 10 days. The most recent releases landed on October 26, 2026 and October 27, 2026 respectively.

## The numbers

| Metric | HRV4Training | Nix Solo |
| --- | --- | --- |
| Price | $9.99 | **Free** |
| Rating | [3.6 (290 ratings)](https://appshunter.io/ios/app/hrv4training/id686923970/reviews) | **[4.8 (68 ratings)](https://appshunter.io/ios/app/nix-solo/id1632680170/reviews)** |
| Number of ratings | **290** | 68 |
| Positive reviews | **60.9% of reviews** | 14.3% of reviews |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 6 weeks | **Every 10 days** |
| Monetization | Paid | **Free** |
| Best chart rank | **#20** | — |
| Size | 35 MB | 65 MB |
| Requires iOS | 15.6 | **15.1** |
| Devices | iPhone, iPod | **iPhone, iPad, iPod, Apple Watch** |
| Age rating | 4+ | 4+ |
| Developer | [A.S.M.A. B.V.](https://appshunter.io/developer/1066843463) | [Nix, Inc.](https://appshunter.io/developer/1625732872) |

## What reviewers say

### HRV4Training

[App page](https://appshunter.io/ios/app/hrv4training/id686923970)

**Currently charting:** #20 Top Paid · Health & Fitness (US App Store)

Quantify stress, balance training and lifestyle, and improve performance with scientifically validated heart rate variability insights. This app accurately assesses HRV using your phone's camera or compatible devices, offering actionable interpretations for optimizing your training plan.

**Highlights:** HRV-based stress quantification, Training and lifestyle balance, Performance improvement insights, Camera-based HRV assessment, Integration with wearables, Training load analysis, VO2max and Lactate Threshold estimation

**Features:** Vision Pro support

**In-app purchases:** none

**What reviewers like**

- 👍 Accurate HRV measurements
- 🚀 Straightforward and easy to use
- 💡 Provides valuable insights for training and recovery
- 👍 Integrates well with other fitness apps
- 👍 Responsive and helpful developer support

**What reviewers complain about**

- 🐛 Inconsistent readings and technical issues
- 🔒 Requires user account and data sharing
- 🔒 Concerns about data privacy
- 🔋 Drains battery when using camera for measurements

**Reported bugs**

- App crashes frequently, especially with iOS updates
- Syncing issues with Strava, TrainingPeaks, and Apple Health
- Camera-based measurements often unreliable or inconsistent

**Requested features**

- Allow multiple measurements per day
- Improve integration with Apple Watch and other wearables
- Add more customization options and data visualization
- Expand support for non-athletic use cases


### Nix Solo

[App page](https://appshunter.io/ios/app/nix-solo/id1632680170)

Monitor personal fluid and electrolyte losses in real-time during workouts. This app provides insights into sweat composition and hydration needs based on individual biology, using data from a companion biosensor.

**Highlights:** Real-time fluid and electrolyte loss monitoring, Personalized sweat composition insights, Correlates sweat data with environmental factors (Nix Index), Post-workout Sweat Intelligence reports, Integration with Apple Watch and Garmin devices, Workout type and hydration input

**Features:** macOS Compatibility, Apple Watch app, Vision Pro support

**In-app purchases:** none


## Frequently asked questions

### Is HRV4Training free?

HRV4Training costs $9.99, with no in-app purchases.

### Is Nix Solo free?

Nix Solo is free to download, with no in-app purchases.

### Which has better reviews, HRV4Training or Nix Solo?

Nix Solo is rated higher. HRV4Training averages 3.6 out of 5 from 290 ratings, while Nix Solo averages 4.8 from 68 ratings.

### Do HRV4Training or Nix Solo have ads?

Neither HRV4Training nor Nix Solo shows ads.

### Which is updated more often, HRV4Training or Nix Solo?

HRV4Training ships an update every 6 weeks, and Nix Solo every 10 days. Most recently, HRV4Training was updated on October 26, 2026 and Nix Solo on October 27, 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.*