Background <p>Annual fitness assessments are performed during group exercise therapy for people with axial Spondyloarthritis (axSpA) living in Switzerland. The core strength test (CST) is time-consuming, and interpretation limited. Thus, the objectives were to 1) compare the CST-performance of people with axSpA and healthy controls, and 2) evaluate if hand grip strength can be used as a proxy for core strength.</p> Methods <p>Routinely gathered data of people with axSpA was used and data from healthy controls collected. Differences in strength were investigated using Welch Two-sample t-tests or Fisher’s exact tests. The associations between grip and core strength were explored through pairwise Pearson correlations (r). Further, a linear regression model was fitted to data of people with axSpA with grip strength as the response variable, and ventral, dorsal and lateral core strength endurance, age and sex as predictors.</p> Results <p>Data from 160 healthy controls (50% male, mean age 59.3 (SD 11.47) years) and 112 people with axSpA (58% male, mean age 57.7 (SD 12.1) years) was included. People with axSpA showed lower core strength endurance (sec) than the controls: ventral core strength mean difference −28, <i>p</i> &lt; 0.001; lateral core strength mean difference −17, <i>p</i> &lt; 0.001; dorsal core strength mean difference −39, <i>p</i> &lt; 0.001, and lower grip strength −3.7, <i>p</i> = 0.012. The linear regression model with hand grip as response and core strength, age, and sex as predictors explained 44% of the variability.</p> Conclusion <p>People with axSpA showed substantially lower core muscle strength endurance than healthy controls. Core strength measures have only marginal effects on grip strength in people with axSpA. Therefore, grip strength is not appropriate to be used a s a proxy for core strength in people with axSpA and healthy people.</p> Clinical trial number <p>Not applicable.</p>