Discussion

Out of 64 873 apps in the categories we searched, 482 apps were found with the keywords used. Eighteen apps met our inclusion criteria and for only four apps with supporting evidence were found in the scientific literature.

Although we performed our search for apps as systematic as possible, we must assume that our search did not include all apps of potential interest. The iTunes search engine is not built for a rigorous scientific search, but for user comfort. It is unknown how the iTunes search engine fetches apps and arranges results after a search. Furthermore, relevant apps might not have been included because they may not have been tagged with the keywords we used for our search. App developers are required to provide a limited number of self-selected keywords when submitting an app to the iTunes Store. Apps of potential interest may have been tagged with other keywords.

Out of 18 included apps, we found four apps with a certain level of evidence-based information. The use of this evidence was different for these apps. The neuromuscular balance intervention presented in the app ‘Ankle’ was based on the outcome of a cost-effective randomised controlled trial. This app was developed specifically to implement this evidence-based exercise programme. The app ‘Ankle’ clearly stated its scientific source. ‘Elastoplast’ was produced as a commercial app, with the goal to familiarise the public with common applications of tape and—arguably—by coincidence contained some evidence-based statements. ‘Elastoplast’ also holds statements, for which no evidence was found and no reference to literature was provided within the app. The ‘iPrevent ACL injuries’ home screen contained the sentence ‘ACL injury prevention techniques’ and only contained the option to play a narrated video. This 18 min video showed a warming-up, stretching, strengthening, plyometrics, agility and cool-down routine. Although the app clearly stated a preventive measure in the app name, it was difficult to find preventive advice within the app, since there was only the option to play the video. When used, the narrated referral to a preventive measure can be overlooked easily. The medical iRehab series are apps with the same functional layout for different injuries, not all covering SPRIs. All iRehab apps contained a section on ‘prevention strategies’. Within this sections 3–4 omnipresent, but mostly not evidence-based, preventive tips were provided. It seems as if some of the preventive claims stated in the medical iRehab series were evidence based by coincidence.

While our main goal was to review the app content, we think that user experience is equally important for an app to reach its goal. In our opinion user experience consists of, but is not limited to, multiple factors including price, presence of bugs, the need to retrieve videos or information online, the presence of advertorials and substantiating to the statement made in the app name, description or content. We included paid apps that gave proven untrue information, crashed when playing a video and contained advertorials. We also included apps, which announced a preventive measure before downloading, but when app content was analysed the preventive measure could not be retrieved. This reduces the user satisfaction and might decrease the app use. We think it is not only important to provide evidence-based content, but also a user-friendly app. An app stating measures to prevent SPRIs should contain evidence-based content and should have a good form and function.

The app ‘How to prevent DOMS’ contained a preventive claim and directed the user to literature that should support their claim. However, when the cited literature was reviewed, the claim could not be extracted. In our opinion, this app tried to create a false sense of security, by citing literature that can be difficult to understand by the untrained reader.

The iTunes App Store provides its costumers the possibility to rate the apps through the ‘costumer rating’ system. We found that only nine of 18 apps had a costumer rating. With half the apps not rated we could not use this rating to compare the apps. Also the rating did not reflect the scientific base for the app content, since average user App Store rating for all apps was higher than for evidence-based apps. Also, user App Store ratings are gameable by marketers, and are therefore less reliable. We tried to overcome this by also including the Appsfire score. This score is not directly based on user critics, but claims to implement more objective data. Although the build-up of the Appsfire score is not completely transparent and its intentions are commercial, it provided an opportunity to compare all apps on an equal basis. Amplitude of the Appsfire score did not reflect the availability evidence and, thus, the content quality of reviewed apps. From this we conclude that there is a discrepancy between user experience and quality of content. Here we have a lot of ground to cover by generating apps that include high-quality content in a useable and appealing package. Simply providing evidence in an app is apparently insufficient to grasp the full potential of implementation of evidence in this way.

The apps containing evidence-based advices were, on average, lower priced and had a lower user rating. It seems that developers produce apps, which despite the lack of supporting evidence, are still downloaded by costumers. This might be because they are found easier and/or because commercial app developers understand the iTunes search engine better than scientists. Most developers seem to be driven more by a commercial than a scientific goal. This commercial goal can be achieved through developing an app that has to be paid for by the costumer. Another way to gain profit from an app is by propagating certain products. For instance, ‘Elastoplast’ was produced by ‘Beiersdorf’, which is a worldwide producer of medical dressings.

While conducting the search for apps in the iTunes store, we found apps that did not strictly meet our inclusion criteria, but did give the impression that they will help the costumer to prevent SPRIs. An example was an app that stated to contain content which a novice barefoot runner should read before commencing. When the content was reviewed no SPRI preventive tips were available.

Also, some apps that appeared to help prevent SPRIs, did not cover a SPRI. For instance, one app covered a golfer’s elbow and another app covered a tennis elbow. People playing golf or tennis are not more likely to develop a golfer's or tennis’ elbow than the normal population. Development of a golfer’s and tennis elbow is associated with movements of the elbow that incorporate force, repetition and vibration,20 and are common also among working age adults.21

The key strength of this study is that it is the first study to review apps claiming to contain content to prevent SPRIs. Mobile app use has increased from 43 min daily in June 2009 to 94 min daily in December 2011.22 Therefore, it is important that this review was done rigorously, so that a foundation can be made for the implementation of strategies to prevent SPRIs through mobile applications.

A limitation of the study is that the App Store search engine is not made for a rigorous scientific search as needed for this review. After each search query each app had to be checked for category since it is not possible to arrange search results by category. Therefore, it is likely that we did not include all the apps that state preventive measures. Another limitation is the absence of evidence for some preventive claims. It is possible that the preventive claims and accompanying sports injuries have not been scientifically evaluated and therefore there is absence of evidence.