HIIT 4x4 vs SolWalks
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
HIIT 4x4
This app guides you through High Intensity Interval Training (HIIT) workouts using your heart rate as a percentage of your Maximum Heart Rate (MHR). It features a speedometer-style dial to monitor your heart rate zones and provides chimes to keep you in target.
- Heart rate zone monitoring
- Speedometer-style dial
- Warning chimes for out-of-zone heart rate
- Workout history storage via Apple Health
- Customizable MHR calculation
- Structured 4x4 HIIT program
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HIIT 4x4 is an Apple Watch exercise monitoring app for High Intensity Interval Training (HIIT). The app sequences exercise between high and low intensity intervals. The intensity of the exercise is measured as a percentage of a person's Maximum Heart Rate (MHR). The HIIT 4x4 intervals are as follows: - 10 minutes warmup at 60% MHR - 4 minutes high intensity at 90% MHR - 3 minutes low intensity at 70% MHR - repeat high-low intervals 4 times (4 high intensity intervals of 4 minutes each = 4x4). HIIT 4x4 uses a speedometer type dial to display heart rate. When the arrow is in the green zone then your heart rate is within the interval target. If the heart rate later falls out of the target range, warning chimes are issued until back in range. Each person's MHR is different, and changes with age. A commonly used formula for MHR is 220 - age in years. A more accurate number can be discovered by using a heart monitor during all out exercise and observing the highest heart rate achieved. HIIT 4x4 stores your workout history using Apple Health. HIIT 4x4 is based on the High Intensity Interval Training 4x4 program developed by the Norwegian University of Science and Technology's Cardiac Exercise Group.
SolWalks
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SolWalks is a tool that helps you develop a habit of taking outdoor walks at the time intervals most efficient to synchronize your circadian clock. In the early 2000s, a type of photosensitive cell called ipRGC was discovered in the human eye. These cells are involved in registering the ambient light illuminance on a subconscious level. It is proved that this signal is the main way to synchronize the body's circadian clock. Spending most of the day indoors and using artificial light frequently can lead to desynchronization of your circadian clock, impaired sleep, increased fatigue, and a depressed mood. SolWalks has a built-in light meter that will allow you to assess the ambient light illuminance, in a similar manner as it happens on a subconscious level. The app is integrated with HealthKit. It visualizes your HealthKit walks data, raising your awareness of the time you spent outside and motivating you to stick to the habit of walking at the optimal time of the day. Terms of use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
Screenshots
Verdict
The clearest difference is price: SolWalks at Free against HIIT 4x4's $9.99. SolWalks also leads on update cadence (every 2 weeks vs every 5 months). HIIT 4x4's advantage is device support (3 vs 1). On ads, in-app purchases and iOS requirement there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
SolWalks is free to download; HIIT 4x4 costs $9.99 up front. Neither carries in-app purchases, so what you see is what you pay.
HIIT 4x4 ships an update every 5 months, SolWalks every 2 weeks. The most recent releases landed on November 2, 2026 and November 7, 2026 respectively.
| Parameter | HIIT 4x4 | SolWalks |
|---|---|---|
| Price | $9.99 | Free — better |
| Rating | 1.0 (1 ratings) — better | — |
| Positive reviews | 0.0% of reviews | — |
| Number of ratings | 1 — better | — |
| Update frequency | Every 5 months | Every 2 weeks — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Paid | — |
| Devices | iPhone, iPod, Apple Watch — better | iPhone |
| Requires iOS | 15.0 — better | 16.2 |
| Further details — not scored | ||
| Size | 2 MB | 4 MB |
| Age rating | 12+ | 4+ |
| Developer | Eastridge Technology | Evgeniy Basistyi |
In-app purchases
HIIT 4x4
No in-app purchases
SolWalks
No in-app purchases









