Apple has been forced to drop a number of health-related features from the upcoming Apple Watch due to issues with the built-in sensors despite over four years of research, development and testing.

Originally, Apple executives planned for the Apple Watch to incorporate sensors that would monitor heart rate, blood pressure and stress levels, making the Apple Watch not just an extension of the iPhone, but a state-of-the-art health and fitness monitoring device.

However, variables such as the tightness of the band, skin moisture levels and even the hairiness of the wearers arms proved too difficult to compensate for, and the proposed sensors were judged as too inconsistent to be included.

According to the Wall Street Journal, Apple was also keen to avoid including any health-related features that would result in regulatory scrutiny, with data privacy and protection an increasing concern, especially when it comes to health and biometric data.

As a result, the devices focus has shifted back towards being a companion for the iPhone, with notifications and key features accessible through the Apple Watch, rather than emphasising the fitness elements that do remain.

Despite the loss of these features, Apple is still predicting the device will be a success, with 6m units ordered for Q2, when the smartwatch is expected to launch, equivalent to the initial launch of the iPad.

With less than 1m Android Wear devices sold last year, such large orders are a clear indicator that Apple thinks there is a market for the device, and given the buzz surrounding the device and Apples trend for successful launches, it is likely they are right.