Background: Submaximal fitness tests (SMFT) outcome measures are frequently collected with a wide array of technologies and methodological approaches. Purpose: To examine the test-retest reliability of various SMFT outcome measures derived from different protocols and analytical techniques. Methods: Twenty-six semi-professional adult soccer players performed three SMFT protocols, including two continuous (3 min, 11 and 12.8 km·h−1) and one intermittent (4 × 50m, 18 km·h−1) twice, each separated by seven days. Heart-rate (HR) indices (exercise HR, HR recovery), scapulae-mounted (PlayerLoad vector magnitude), and foot-mounted (flight- and contact-time, stride length) micro-electrical mechanical systems (MEMS) derived variables were collected using different timeframes and analytical approaches adopted in the literature and practice. Absolute reliability was quantified as the group mean difference (MD), typical error of measurement (TE), also expressed as the coefficient of variation (CV; where appropriate) and standardised units (i.e., d). Intraclass correlation coefficient (ICC) was used to quantify relative reliability. Results: The highest degrees of reliability were evident for exercise HR (TE: 1.0 to 1.6 % points), the vertical component of PlayerLoad (expressed in arbitrary units; CV: 5.5 to 7.0%) and contact-time (CV: 1.5 to 3.0%). These estimates were not influenced by SMFT protocol or analytical approach. All other measures displayed poorer reliability and/or were different between protocols and analytical methods. Conclusions: SMFT protocols impact upon the test-retest reliability of various outcome measures; however, exercise HR, PlayerLoad vertical and contact-time (derived from foot-mounted MEMS) appear to have stable measurement properties to assist the assessment of aerobic capacity and lower-limb neuromuscular status, respectively.