Today, I want to talk about a piece of gear that's become a pretty important part of my daily routine: The Coospo HW9 heart rate monitor. I've been using it a lot lately, especially with the Pulse Range Monitor app on my Android phone (and even my TicWatch Pro Wear OS device!).
Why I Love the HW9 (and Its Quirks)
One of the coolest features of the HW9 is its haptic alarm. You can set it to vibrate when your heart rate hits a certain level, which is super handy. It also does heart rate variability (HRV), which is a game-changer for me. I often struggle with understanding my moods or why I might be feeling anxious or stressed. HRV helps me check in with myself and decide if I need to do some breath work or other stress-reducing activities.
Now, my primary PPG armband device is actually the Scosche Rhythm 24. It's great because it has internal memory and records in a simple spreadsheet format, but its battery only lasts about 12 hours with continuous recording. To get around that, I'd need two of them for 24/7 tracking. The Hepatic Heart Rate Alarm helps when I'm working in the desert summer heat. Often I'll get focused on a work related task and not notice that my body is getting too hot. As a diabetic that leads to real problems. This is where the Hepatic alarm comes into play. When it goes off I know it's time to slow down and cool off and drink water. An increased heart rate is one of the first signs that your body is experiencing an increased heat load as blood vessels will dilate and the heart needs to beat faster to compensate. I have mine set to 120 BPM…. Everyone will have to discover their own rate for this type of use.
This is where the Coospo HW9 truly shines as a backup! It boasts a 30-hour battery life and dual Bluetooth channels. While it doesn't have internal memory, its long battery life and HRV capabilities make it an excellent partner for my Android phone. Plus, when I'm working out, the HW9's LED indicator blinks different colors to show me which heart rate zone I'm in – a neat visual cue!
Other Handy Features
The HW9 also has a small, compact proprietary charger that's easy to pack. It charges up pretty quickly too! You can also buy different armbands for it. I'm using the original one now, but I'd suggest picking up a few extra elastic armbands since they tend to wear out after about six months of daily use.
My Ideal Monitor vs. Reality
While the HW9 isn't absolutely perfect for my needs, it's a solid backup. I actually prefer it over the Polar Verity Sense, even though the Verity Sense has memory and a long battery life, because the Verity Sense doesn't do HRV.
Ideally, I'd love a PPG device that could do HRV readings even when I'm in motion (like in a car or on an airplane), has 24-hour memory for heart rate, and even continuous HRV recording to memory. I know that last bit is a bit of a stretch given the current limitations of PPG devices when you're not perfectly still, but a guy can dream, right? The Sonia Rhythm 24 does excel at HRV while in motion, which is a big plus for me.
Let's Talk About Cadence Lock on PPG Sensors and why it's a challenge for the HW9
It’s a common issue with PPG (photoplethysmography) heart rate sensors, like the Coospo HW9, especially when you're moving around a lot. This phenomenon is often called "cadence lock."
Let me break down what's happening and why the HW9 might be giving you inaccurate readings in these situations.
What is Cadence Lock?
PPG sensors work by shining an LED light into your skin and measuring the light reflected back. The amount of light reflected changes as blood flows through your capillaries with each heartbeat. This allows the sensor to detect your pulse.
Cadence lock occurs when the motion of your body, rather than your actual heart rate, influences the PPG sensor's readings. Instead of picking up the subtle changes in blood volume from your pulse, the sensor "locks on" to the rhythmic movements of your arm or wrist.
Think about it this way:
* Running/Exercise: When you're running or exercising, your arms swing, and your body moves rhythmically. This movement can cause the sensor to bounce slightly on your skin, or it can introduce "noise" into the light signal that mimics a pulse. If your running cadence (steps per minute) is close to your heart rate, the sensor can easily get confused and report your cadence as your heart rate. This can lead to unusually high or low readings that don't reflect your actual exertion.
* On a Train/Moving Vehicle/Airplane: Similar to exercise, the vibrations and subtle movements of a train or car can interfere with the PPG sensor. The constant, rhythmic jostling can create a "signal" that the sensor misinterprets as your heartbeat.
* Using a Keyboard: Even something as seemingly small as typing on a keyboard can create enough repetitive wrist and hand movement to throw off a PPG sensor. The small, quick movements can create noise in the signal that the sensor mistakes for a pulse.
Why does it happen? The Science Behind the "Noise"
Here's a deeper dive into why PPG sensors are susceptible to cadence lock:
* Motion Artifacts: Any movement of the sensor relative to your skin can cause "motion artifacts." This means that the light reflecting back to the sensor is influenced by external movement, not just blood flow. This "noise" can overwhelm the actual heart rate signal.
* Sensor Placement and Tightness: If the sensor isn't snug against your skin, even tiny movements can cause ambient light to creep in under the sensor, further corrupting the signal.
* Frequency Overlap: When your movement cadence (e.g., steps per minute) is very close to your actual heart rate, it becomes challenging for the sensor's algorithms to differentiate between the two signals.
* Blood Flow Dynamics: While PPG aims to detect changes in arterial blood flow, some theories suggest that in certain conditions (like cold weather causing vasoconstriction or the presence of condensation on the sensor), the sensor might pick up more changes in venous blood flow. Veins are a lower-pressure system and their hemodynamics are more easily influenced by arm motion, contributing to cadence lock.
What You're Seeing with Your HW9
When your HW9 gives inaccurate results during these activities, it's very likely experiencing cadence lock. You might see your "heart rate" suddenly jump to match your steps per minute while running, or fluctuate wildly on a train, or give a very consistent, but incorrect, reading while typing.
What Can You Do?
While the Coospo HW9 is a great backup, and you appreciate its HRV capabilities, optical sensors on the arm or wrist do have these inherent limitations. Here are some strategies to mitigate cadence lock:
* Tighten the Armband: Make sure the HW9 is snug, but not uncomfortably tight, on your arm. It should not be bouncing or sliding around.
* Move It Up Your Arm: Often, wearing the armband a bit higher on your forearm (away from the wrist bone) can provide a more stable reading as there's less bone and more muscle/flesh for the sensor to pick up consistent blood flow.
* Clean the Sensor: Ensure the optical sensor on the back of the HW9 is clean and free of sweat, dirt, or lotions.
* Consider a Chest Strap for Critical Readings: For activities where highly accurate heart rate data is crucial (like intense workouts or specific training zones), a chest strap heart rate monitor (which uses ECG technology, the gold standard) will almost always be more accurate and immune to cadence lock. You mentioned the HW9 is your backup, and it's excellent for that and continuous monitoring.
* Be Aware of Environmental Factors: Cold weather can sometimes exacerbate the issue due to vasoconstriction.
* Analyze the Data: If you see your heart rate suddenly matching your steps per minute, or becoming unnaturally stable during high-movement activities, you can reasonably assume it's cadence lock and disregard that particular data point.
It's a balance between convenience and accuracy with PPG sensors. For general all-day tracking and non-critical data, the HW9 is fantastic, but for those specific high-motion scenarios, understanding cadence lock helps you interpret the data more effectively.
The Coospo Line-up
I've tried other Coospo PPG devices, but they just don't have the features of the HW9. Some even have awkwardly placed on/off buttons that can accidentally turn off the unit. Honestly, I think the HW9 is probably the best in the Cospo line, and you can often snag one for under fifty bucks, which is a fantastic deal!
For now, the HW9 is my go-to heart rate sensor. I'm also planning to try pairing it with the "Sleep as Android" app for my nightly HRV and heart rate readings. Fingers crossed that works out!
That's all for today's blog post!
