Period Calendar/Tracker has the best health and fitness app according to the new report, The 2016 State of The U.S. Health & Fitness Apps Economy, by research group Application Resource Center, a subsidiary of app quality and testing company Applause App Quality Inc.

With about 8,000 health and fitness apps between Google Play and the Apple App Store, the research group analyzed 65 of the most popular health apps, which it selected based on the number of consumer reviews an app drew between the two app stores. Each app had at least 10,000 reviews. It then rated health and fitness apps in the following categories: fitness, medical, nutrition, stress relief and women’s health apps.

ARC assigned a numerical score to each app of 0 to 100 based on such factors as ratings in the store, usability, privacy, satisfaction, performance, security, stability, elegance and content, says Ben Gray, digital experience analyst at Application Resource Center and the author of the report.

The average app quality score for the 65 apps was 66, which is higher than other verticals ARC has measured. For example, travel apps earned an average app quality score of 47 and finance apps 64. Gray attributes this to the stiff competition in health and fitness mobile apps.

“The health and fitness apps economy is insanely competitive, and app quality serves as a differentiating factor in standing out in the eyes of consumers,” Gray says.

Menstrual cycle app Period Calendar/Tracker earned a score of 94.5, and was the No. 1. health and fitness app out of all the categories, and another menstrual cycle app, Period Tracker, app had a score of 88.5 and ranked No. 3 overall.

Of all the health app categories, women’s health apps ranked the highest with an average score of 81. Fitness apps ranked the lowest with an average score of 68.

Sleep aid and meditation sounds app Relax Melodies was the highest-ranked stress relief app, with a score of 88.5 and ranked No. 2 among all the apps. Other app category winners were: Muscle building coach app StrongLifts (86.0) in the fitness category; prescription drug price comparison and coupon app GoodRx (84.5) in the medical category; and Water Drink Reminder (85.0) in the nutrition category.

The apps that rank high help people in their everyday lives, Gray says. For example, Relax Sounds lets consumers customize sounds to help their child get to sleep within minutes, making it a useful app for tired parents.

Apps that ranked the lowest overall included health tracking wearable companion app FitBit (49.5), weight loss app Weight Watchers Mobile (47.0), fitness tracking app Google Fit (37.0) and Garmin fitness devices companion app Garmin Connect Mobile (21.0).

Many of these apps work with wearable devices, which contributes to their low rankings, Gray says. Since the apps are dependent on another device, more could go wrong. For example, a consumer could be using an old fitness band, or hasn’t updated the app, and the syncing might not be working properly.

“Apps that are dependent on connecting with external resources, such as fitness bands and heart rate monitors with health and fitness apps or digital rights management systems with media and entertainment apps, for example, are at an immediate disadvantage in delivering highly-rated customer experiences,” Gray says.

By category, lowest-ranking apps include Pregnancy & Baby (67.5) in women’s health, sleep-tracking app Sleep Time (64.0) in stress relief, WebMD (63.0) in medical, Weight Watcher Mobile (47.0) in nutrition, and Garmin Connect Mobile (21.0) in fitness. Many of the lower-ranked apps struggled with inaccurate notifications and connectivity issues, Gray says.

Some apps in the middle of the pack are gaining ground. For example, fitness tracking wearable Jawbone’s companion app UP improved 12.5 points on ARC’s scale between December 2014 and December 2015 to 54.0. Gray attributes this to feature improvements, such as a newly introduced Smart Coach, that serves as an in-app health advisor.