When it was announced in 2014, the Apple Watch included only a limited array of health sensors -- heart rate and activity tracking capabilities mainly -- despite Apple hires and rumors that suggested more. A Wall Street journal article last year gave some insight into the disconnect, saying that accuracy concerns plagued the project. Now a Fast Company interview with Bob Messerschmidt, a former Apple executive who left in March to start blood-testing startup Cor, has shed some further light on what was happening behind the scenes at Apple.

According to Messerschmidt's account, it was not primarily accuracy concerns that held his team back in the creation of the Apple Watch's heart rate sensor, the most advanced health sensor that did make it to the device. Instead, it was the design team, who had a lot of pull.

"I went to a meeting and said 'I’m going to put sensors in the watch but I’m going to put them down here (he points to the underside of the Apple Watch band he’s wearing) because I can get a more accurate reading on the bottom of the wrist than I can get on the top of the wrist,'" Messerschmidt told Fast Company. "They (the Industrial Design group) said very quickly that 'that’s not the design trend; that’s not the fashion trend. We want to have interchangeable bands so we don’t want to have any sensors in the band.' Then at the next meeting I would go 'We can do it here (on top of the wrist) but it’s going to have to be kind of a tight band because we want really good contact between the sensors and the skin.' The answer from the design studio would be 'No, that’s not how people wear watches; they wear them like really floppy on their wrist.' That creates a set of requirements that drives you toward new engineering solutions."

Messerschmidt doesn't seem bitter, however. He feels that despite the design team forcing them to be more creative, the company still created a heart rate sensor to be proud of.

"I’m so proud of my contribution to the heart rate sensor because it’s generally discussed as the most accurate sensor that Apple has ever put in a product," he said in the interview. "It had to be, because you look at the trials and tribulations of a company like Fitbit. Fitbit is great, don’t get me wrong, but they are wading through lawsuits right now about the accuracy of the heart rate sensor. They didn’t put enough thought into the use cases.”

(It's worth noting that one company that's suing Fitbit over its heart rate tracker, Valencell, is also suing Apple.)

We may never know how much design considerations held back the other health sensors considered for the Apple Watch, but the interview makes clear the importance to Apple of striking that balance between clean, user-friendly design and top-of-the-line technology. Messerschmidt argues that erring on the side of user-friendliness is a secret of Apple's success.

"If you look at products like the iPhone or the iPad there aren’t too many totally new technologies included in those products," he said in the FastCo interview. "The real elegance and differentiation doesn’t have a lot to do with the technology idea itself; it’s about the packaging and the value add it gives to people. Those big (new technology) ideas generally happen elsewhere, and they happen earlier. Virtual reality is a good example. Why hasn’t Apple jumped into VR? It’s because nobody really knows whether there’s really a 'there' there. I don’t. Apple’s interested in products where everybody’s going to get some benefit out of it."

Be sure to check out the whole interview, which includes some other interesting insights about Apple's corporate culture.