{
  "abstract": "BackgroundDigital nudging strategies are increasingly implemented to promote physical activity; yet, evidence from real-world fitness settings remains limited. The early membership period in fitness centers is characterized by high dropout rates, emphasizing the need for formative evaluations that clarify behavioral mechanisms underlying exercise engagement. ObjectiveThis study aimed to evaluate the formative impact of WhatsApp (Meta Platforms, Inc)-based digital nudges on objectively measured weekly gym visits among new fitness club members and to examine behavioral determinants associated with exercise engagement. MethodsThis controlled intervention study used a 2-parallel-group design with quasi-random individual allocation conducted separately within 2 fitness clubs. The complete-case sample comprised 61 new gym members (mean age 29.05, SD 8.06 years; 21/61, 34.4% female), including 27 participants in the intervention group and 34 in the control group. During the 3-week intervention period, participants in the intervention group received brief digital nudges through designated WhatsApp groups. The messages were developed according to the Easy, Attractive, Social, and Timely (EAST) framework. Participants in the control group received no nudge messages. Gym visits were recorded electronically over 12 weeks through the fitness clubs’ computerized entry systems. Self-reported measures included exercise self-efficacy, habit strength, and exercise adherence. Statistical analyses included descriptive statistics, longitudinal analysis of weekly gym attendance using generalized estimating equations (GEE), correlation analyses, and exploratory regression analysis. ResultsLongitudinal GEE analysis showed a significant decline in weekly gym attendance over time (b=–0.074, SE 0.016; PP,PPrrrPR2P ConclusionsWeekly gym attendance declined significantly over the 12-week follow-up period, but the rate of decline did not differ significantly between the intervention and control groups. However, exercise adherence, exercise self-efficacy, and exercise habit strength were positively associated with more frequent attendance, and participants attending at least twice weekly reported greater self-efficacy and stronger exercise habits. These exploratory findings identify potentially relevant behavioral factors for future adherence interventions.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "name": "Maor Gabay",
      "orcid": "0009-0005-9837-6894"
    },
    {
      "name": "Ofer Levi",
      "orcid": "0000-0001-7523-642X"
    },
    {
      "name": "Lupsa Marius Matichescu",
      "orcid": "0000-0002-8381-9454"
    },
    {
      "name": "Mihaela Oravitan",
      "orcid": "0000-0002-6868-0837"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/7rayfb021vh0c.bib",
  "cited_by": 0,
  "doi": "10.2196/93800",
  "fulltext_url": "https://formative.jmir.org/2026/1/e93800",
  "id": "7rayfb021vh0c",
  "issns": [
    "2561-326X"
  ],
  "landing_url": "https://doi.org/10.2196/93800",
  "language": "en",
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "lcc",
      "R"
    ],
    [
      "openalex",
      "3202|Behavioral Health and Interventions"
    ]
  ],
  "openalex": "W7204046498",
  "pdf_url": null,
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-23",
  "publisher": "JMIR Publications",
  "ris": "https://research.draconitic.com/paper/7rayfb021vh0c.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T13:44:21Z",
      "native_id": "3019bb40d8684346a3a93259e33f3912",
      "source": "doaj",
      "url": "https://doi.org/10.2196/93800"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "lcc:R",
      "subfield": "general"
    }
  ],
  "title": "Digital Nudges Among New Gym Members: Controlled Formative Evaluation of Gym Attendance, Exercise Self-Efficacy, Habit Strength, and Exercise Adherence",
  "title_text": "Digital Nudges Among New Gym Members: Controlled Formative Evaluation of Gym Attendance, Exercise Self-Efficacy, Habit Strength, and Exercise Adherence",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T13:44:21Z",
  "url": "https://research.draconitic.com/paper/7rayfb021vh0c",
  "venue": "JMIR Formative Research",
  "versions": []
}