What is the difference between PEAKVO2 and Seconds?

Seconds is an interval timer: you build and modify your own Tabata, HIIT, and circuit timers, with a full-screen display and spoken cues, and it times whatever you program. PEAKVO2 is a VO2 max training app: it ships eight ready-made, evidence-based endurance protocols like the Norwegian 4x4 with heart rate zones, automatic phases on your wrist, and a VO2 max trend over time. Seconds is a flexible timer tool; PEAKVO2 decides the training and tracks the result.

Should I use PEAKVO2 or Seconds?

Use Seconds if you want a best-in-class, endlessly configurable interval timer to run any Tabata, HIIT, or circuit workout you design yourself. Use PEAKVO2 if your goal is specifically VO2 max and you want proven endurance protocols run for you, with the heart rate zones they need and your VO2 max tracked over time. Seconds times what you tell it; PEAKVO2 gives you the workout and the number to watch.

Does Seconds track VO2 max or include the Norwegian 4x4?

Seconds is an interval timer and does not advertise VO2 max tracking or named endurance protocols like the Norwegian 4x4. You can build a 4x4-style timer in it, but you set the intervals and would track heart rate zones and VO2 max yourself elsewhere. PEAKVO2 ships the Norwegian 4x4 and seven other protocols ready to run, with the heart rate zones they depend on and a VO2 max estimate tracked over time.

Which is cheaper, PEAKVO2 or Seconds Pro?

Seconds is free in its basic version, and Seconds Pro is a one-time purchase of $7.99. PEAKVO2 gives you three full workouts free, then unlocks its whole library for $0.99 per month, $9.99 per year, or $19.99 for lifetime. Seconds Pro is the cheaper one-time price for a pure timer; PEAKVO2 costs a little more but includes the protocols, heart rate zones, and VO2 max tracking a bare timer does not.

Which is better for Apple Watch interval training?

Both run standalone on Apple Watch with haptic cues and no phone needed. The difference is what runs on the wrist: Seconds runs the timers you build, while PEAKVO2 runs ready-made VO2 max protocols with full-screen color-coded phases and the heart rate zones those protocols depend on. For a flexible timer, Seconds is excellent; for guided VO2 max training, PEAKVO2 is purpose-built.

PEAKVO2 vs Seconds Interval Timer: Timer or Training App?

By Cristian Serb · Updated August 17, 2026

A close-up stopwatch, the classic tool for timing workout intervals

Run these workouts on your iPhone, or hands-free on Apple Watch. Get PEAKVO2

Seconds is the classic interval timer: you build your own Tabata, HIIT, and circuit timers and it runs whatever you program, on iPhone and Apple Watch. PEAKVO2 is a VO2 max training app that ships ready-made endurance protocols like the Norwegian 4x4, guides them with heart rate zones, and tracks your VO2 max. Pick Seconds for a flexible timer you configure; pick PEAKVO2 for guided VO2 max training.

Seconds is one of the best interval timers ever made, so this is not about which is better overall. It is about the difference between a timer and a training app: whether you want to design the workout yourself or have proven protocols handed to you and your progress tracked.

PEAKVO2 vs Seconds at a Glance

	PEAKVO2	Seconds
What it is	VO2 max training app	Interval timer
What you run	Eight ready-made endurance protocols	Timers you build or adapt from templates
Named VO2 max protocols	Norwegian 4x4, Tabata, HIIT 30/30, and more, built in	Not advertised; build your own
VO2 max tracking	Yes, trend over time	No
Heart rate zones	Tied to each protocol	Heart rate via Apple Health for calories
Field tests	Built-in beep and Cooper tests	Not the focus
Apple Watch	Standalone, full-screen phases, haptics	Standalone, full-screen display, haptics
Platform	iPhone and Apple Watch	iOS and Android
Price	3 workouts free, then $0.99/mo, $9.99/yr, $19.99 lifetime	Free, or Seconds Pro $7.99 one-time

What Seconds Is

Seconds is a highly capable interval timer for iPhone and Apple Watch. It gives you templates for HIIT, Tabata, and circuit training and a quick editor to build your own, with each interval getting its own name, color, and alert. It shows a full-screen, colored, read-from-a-distance display, speaks interval names, can play music per interval, and runs in the background. On Apple Watch it works standalone with haptic cues, and timers you build on the phone sync to the wrist. Its strength is flexibility and polish: if you can describe the intervals, Seconds will run them cleanly.

What PEAKVO2 Is

PEAKVO2 is an interval training app for iPhone and Apple Watch, built around VO2 max. It ships eight validated endurance protocols, the Norwegian 4x4, Tabata, HIIT 30/30, Billat 30/30, Ronnestad 30/15, VO2 Max 3x3, VO2 Max 5x3, and Tempo Run, with full-screen color-coded phases, automatic transitions, a haptic tap at each switch, and the heart rate zones those protocols depend on. It runs natively on Apple Watch with no phone needed, tracks your VO2 max trend over time, and includes built-in beep and Cooper field tests. It is a training app, not a testing service. You do not design the workout: you pick a proven protocol and it runs.

The Core Difference: A Timer vs a Training Program

Seconds answers "run the intervals I give you." PEAKVO2 answers "give me the intervals that raise my VO2 max, and show me the number." That is the whole distinction.

If you already know exactly what session you want, or you invent your own circuits, Seconds is the better tool: it is more flexible and, as a one-time purchase, cheap. But a timer does not tell you which protocol raises VO2 max, does not hold you to the heart rate zones those protocols depend on, and does not track your VO2 max over time. PEAKVO2 does all three, because it is a training app built around one outcome rather than a blank timer. You could rebuild the Norwegian 4x4 in Seconds by hand; you would be recreating what PEAKVO2 ships ready to run, without the zones or the VO2 tracking around it.

Who Each One Is For

Choose Seconds if you want a flexible, polished interval timer to run any Tabata, HIIT, or circuit workout you design yourself, and you like building your own sessions. As a one-time $7.99 purchase, it is a great value tool.
Choose PEAKVO2 if your goal is your aerobic engine: proven VO2 max interval protocols run for you, with the heart rate zones that raise VO2 max and your VO2 max tracked over time. It fits runners, cyclists, and endurance athletes who want the training decided and measured, not just timed.
Use both if you build your own circuits with Seconds and want a dedicated, guided tool for VO2 max work. They sit well together: one is the timer, the other is the program.

Build your aerobic engine with PEAKVO2

Guided VO2 max protocols, the Norwegian 4x4, Tabata, REHIT, and more, on iPhone and Apple Watch, with heart rate zones, automatic phases, and your VO2 max tracked over time. Three workouts free.

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Cristian Serb

I'm the developer of PEAKVO2. I built it because I was doing the Norwegian 4x4 myself and wanted the timing handled on my wrist so I could just train. I took my own VO2 max from about 41 to 51 with it. PEAKVO2 on the App Store.