Viewpoints presented in this blog reflect opinions of the author and do not necessarily reflect positions or policies of ACSM.

Substantial evidence demonstrates the importance of physical activity (PA) for protecting against cardiovascular disease (CVD) and all-cause mortality, but not all physical activity is created equally. In fact, higher intensity physical activity and exercise, which increases heart rate more so than lower intensity exercise, may have greater effect to improve cardiorespiratory fitness and all-cause and CVD mortality.

Recently a new technology, Personalized Activity Intelligence (PAI) was introduced as a means to define optimal levels of PA to protect against CVD and all-cause mortality. Watch the webinar.

Below are some questions from webinar attendees:

Q- Based on the max per day (75 PAI), does this mean that for excessive exercisers, maxing out 7x/wk for a total of 525 PAI, that this would still be in an optimal health range, or is this too high above optimal PAI?

The goal of maintaining 100 PAI or greater across a 7-day window is the optimal prescription for reducing risk of lifestyle diseases. Once you have exceeded 100 PAI, going beyond that does not promote additional risk reduction, but it can certainly improve aerobic performance and metabolic efficiency.

Q- Can one do too much high-intensity training? Can you speak to those who race almost every weekend and move from one sport to another and never take a break (bicycle racer Leonard Zinn, for example, ending up in atrial fib)? I am around many amateurs who race bicycles, then cyclocross, then Nordic skiing and are doing a lot of high-intensity training. Is there a point of detriment? Should there be more periodization?

PAI was developed with the goal of helping people to achieve maximum health benefits and reduce the risk of lifestyle diseases. It is not necessarily a training paradigm for sport. Periodization is certainly important when training to peak performance precisely before a race. Modulating between volume and intensity is important to build your endurance base but also to become accustomed to "race pace."

Q- Can PAI be used like MY Zone for HR tracking in group training sessions?

Absolutely; however, PAI currently isn't available on a group training platform. We are working on some partnerships that will integrate PAI into other systems.

Q- Can you be a bit more detailed about the algorithm that calculates PAI?

PAI uses the individual's Max HR and Resting HR to create a Heart Rate Reserve whereby heart rate intensity is calculated and then converted into a PAI Score. The daily PAI score is scaled across a 7-day rolling window with the optimal goal of staying above 100 PAI. For more detailed information you can review the PAI study that was published in The American Journal of Medicine.

Q- Could PAI be safely used by patients taking medications that affect heart rate, such as beta blockers?

Ultimately, anyone who is at risk should consult a physician before engaging in any exercise program. Since one of PAI's inputs is Max HR, which will be blunted as a result of taking beta blockers, we don't specifically recommend the use of PAI. We are currently exploring PAI for a variety of clinical scenarios which should be made available later in 2018.

Q- Do the older Mio trackers (Fuse, Alpha 2) calculate PAI scores?

The Mio FUSE and Mio ALPHA 2 are able to stream heart rate to our PAI app to calculate PAI scores.

Q- Do you believe some groups may be more motivated by their PAI (younger, participants in circuit training) compared with older individuals or those whose primary exercise is walking. Does it have to be running or can it be cardiovascular exercise of any kind (for example -- step aerobics)?

PAI is ideal for anyone who is interested in leading a healthy lifestyle and who could also use help in understanding how much physical activity is enough to achieve optimal health benefits. It also provides motivation for those who don't exercise very often, encouraging them to be more consistent, since the PAI metric reminds them if they are not doing enough. It can be beneficial to people across all ages and lifestyles, and since it isn't based on steps, any activity can contribute to PAI - as long as it gets your heart rate up. Older individuals who rely on walking as their primary exercise can benefit, as they may learn that they need to increase the pace or incline to get their heart rate up during their walks.

Q- Does PAI coincide with the ATP or Kreb cycle energy system use?

PAI is related to intensity which drives improvements in aerobic performance. Aerobic performance improvements have been directly linked to reductions in lifestyle diseases. So PAI is the personalized dose to improve an individual's VO2 to a level which optimizes risk reduction.

Q- Given the HR variability with wrist-based measurement, is this an accurate way to assess intensity?

Typically, the current generation of optical heart rate sensors are adequate to calculate PAI. You also can stream Bluetooth compatible chest straps to the PAI app if there are further concerns around accuracy.

Q- Has there been research on use of PAI in cardiac rehab patients and their rehab outcomes?

This is currently in progress.

Q- How can I compute my PAI with the watch I already have (Garmin Vivofit Active HR)? Or any other HR watch?

We are working on extending PAI to be compatible with other heart rate tracking devices; however, there is currently no way to calculate PAI beyond using our Mio SLICE product or streaming a Bluetooth compatible device to our PAI app. You can sign up on this page, to be notified when we make PAI available on the Apple Watch® and other devices.

Q- How could physical activity guidelines be revised to consider PAI?

We continue to build strong relationships with the leaders in this space who create physical activity guidelines and hope that someday PAI will become the new standard of measurement of physical activity.

Q- How does the adaptive part of PAI work? That is, when an individual has gains in cardiorespiratory fitness, how will the algorithm adapt to ensure 100 PAI is still giving the same stimulus?

PAI is calculated based on your profile information, Max HR and Resting Heart Rate (RHR). The key metric which ultimately changes with increased exercise is a decrease in RHR. So, as you become more fit, RHR will decrease which results in a larger heart rate reserve (HRmax - HRrest) meaning that it will require more intensity to generate more PAI. The reverse also happens with detraining.

Q- How many days per week are suggested to achieve the 100 PAI per session?

We ensure that users need to exercise a minimum of 2x week to achieve 100 PAI, as a result of the maximum daily limit of 75 PAI. We typically find that individuals exercising for 30 mins/day at a moderate intensity can maintain 100 PAI, but individuals also can do high intensity workouts 2x week and maintain over 100 PAI. PAI gives people flexibility depending on what they like to do, their fitness level, and how it fits into their lifestyle.

Q- How reliable is the heart rate wrist monitor in the wearable Mio SLICE compared to thoracic heart rate monitors?

Typically, the current generation of optical heart rate monitors available on the market, including SLICE, have adequate accuracy to calculate PAI. A typical standard is to be within +/- 5 bpm 90 percent of the time when compared to a chest strap. Wrist-based devices typically perform better in endurance types of activities.

Q- If the PAI score is only generated by looking at heart rate data over the course of a day/week, how are elevated heart rates induced by exercise (good stress) and sickness or other bad stressors differentiated from each other?

Significant amounts of PAI points are only generated at moderate to high heart rate intensities so somewhat elevated heart rates attributed to stress or sickness will not have a meaningful impact on the total PAI score.

Q- Is the intention of this technology to be geared toward a public mainstream gadget, an exercise physiologist or personal trainer use, or clinical use?

The intent is for PAI to become the new standard in activity tracking and lifestyle medicine that becomes adopted and endorsed by practitioners and all parties within the health care industry. Part of this adoption plan is to create an engaging experience for the end user and to make it available through as many devices as possible.

Q- Is there a way to calculate PAI without the device?

Unfortunately, no. Heart rate data is a requirement to calculate PAI. PAI will be available through other devices that track heart rate, beyond SLICE, in 2018.

Q- Is this Mio SLICE waterproof? If so, how does the device correlate to aquatic sports?

Mio SLICE is water resistant up to 30 m and can be used for swimming.

Q- So if you achieved the 100 PAI in 2 days, the benefits are still there?

That is correct; you are maximally protected with a PAI score of 100 or above no matter how frequently you exercise or at what intensity it took to get you there.

Q- The Mio SLICE tracks heart rate. Is it using an infrared sensor? Is that as accurate as wearing a chest sensor?

Mio SLICE uses photoplethysmogram (PPG), 2 green LEDs and 1 optical sensor, to calculate heart rate. A typical standard is to be with +/- 5 bpm 90 percent of the time when compared to a chest strap.

Q- Would exercisers get the same benefit from aerobically vigorous bike riding as running?

Some people cannot tolerate the pounding on the knees that comes with running, so I'm wondering if cyclists would realize similar benefit with respect to morbidity and mortality. The key differentiator to other metrics which quantify physical activity is that PAI uses heart rate to calculate its score. Any activity which elevates your heart rate counts-it is universal.