Reliability and validity of the International FItness Scale (IFIS): A systematic review and meta-analysis

Reliable and valid physical fitness instruments are necessary for population-level surveillance and monitoring. However, lab-based and field-based measures are often impractical in large-scale studies. Self-rated fitness scales such as the International Fitness Scale (IFIS) offer a feasible alternative. Therefore, the aim of this review was to quantitatively synthesize the available evidence on the reliability and validity of the IFIS.

Four online databases (Ovid MEDLINE, SPORTDiscus, EMBASE and PubMed) were searched for papers published prior was performed August 2025. Studies meeting the following criteria were included: (1) published in English, (2) investigated the validity or reliability of the IFIS, (3) no limitation for population subgroups of the included studies. The risk of bias was assessed through the latest version of the COSMIN (Consensus-based Standards for the selection of health Measurement Instruments) Risk of Bias checklist. The random effects model was employed to compute the pooled effect sizes, the heterogeneity of the average effect size was assessed using I² statistic and Q statistics.

After title and abstract screening, 20 records were assessed for full-text eligibility. Of these, 13 eligible studies (9634 participants) were included in this study. Reliability was assessed in 10 studies, and construct validity was assessed in a total of 11 studies (3 assessed the criterion validity). A substantial test-retest reliability was observed for overall fitness (pooled weighted kappa = 0.750, 95%CI = 0.600-0.848, Q = 899.283, I ²  = 98.777), cardiorespiratory fitness (pooled weighted kappa = 0.752, 95%CI = 0.612-0.846, Q = 816.758, I ²  = 98.653%), muscular fitness (pooled weighted kappa = 0.724, 95%CI = 0.630-0.798, Q = 350.584, I ²  = 96.862%), speed-agility (pooled weighted kappa = 0.764, 95%CI = 0.645-0.847, Q = 655.508, I ²  = 98.322%), and flexibility (pooled weighted kappa = 0.725, 95%CI = 0.633-0.796, Q = 335.094, I ²  = 96.717%). The 11studies assessing the construct validity of the IFIS reported that participants who self-rated higher fitness with IFIS had higher objectively measured fitness, but due to different methods used, these results could not be meta-analyzed.

This study shows that the IFIS is a reliable instrument to assess physical fitness in children and adolescents. Acceptable validity was reported across studies, yet could not be meta-analyzed due to diversity in methodologies. More studies are needed to discern its cultural adaptation among different population groups.