The acute effect in performing common range of motion tests in healthy young adults: a prospective study

The study addresses whether repetition-dependent acute effects known from stretching (rapid initial ROM gains followed by diminishing returns and plateau after few repetitions) also occur during the performance of common ROM assessment tests. ROM tests inherently apply a stretching stimulus to muscle–tendon units; thus measurement protocols (number of repetitions, warm-up) may influence outcomes. Current practice lacks standardization, with studies using variable and often unspecified numbers of warm-up trials, repetitions, and rest. The authors hypothesized that ROM tests would exhibit an acute effect analogous to stretching, with a non-linear (logarithmic/exponential) pattern of ROM gain across repeated trials, and aimed to determine if plateau formation occurs and to provide recommendations for standardized assessment protocols.

Prior work on stretching demonstrates acute effects within the first few repetitions for ROM, stretch tolerance, and passive torque, with the greatest gains early and diminishing improvements thereafter; practical recommendations often suggest four to five repetitions due to minimal subsequent gains. ROM assessments commonly use goniometers, inclinometers, or tape measures and measure active or passive ROM, with passive torque, stretch tolerance, and isometric force influencing measured ROM. However, literature reveals heterogeneous ROM testing protocols regarding warm-up and number of repetitions, including interventions, normative surveys, and reliability studies, often with one to three repetitions and minimal or unspecified warm-ups. Evidence from stretching suggests a logarithmic behavior of ROM gains, but whether this occurs in ROM test execution was previously unclear.

Design: Prospective pilot study. Participants: 22 healthy sports students (10 male, 12 female), mean age 25.3 ± 1.94 years; height 174.1 ± 9.8 cm; weight 66.6 ± 11.3 kg; BMI 21.9 ± 2.0 kg/m². Exclusions: prior relevant orthopedic surgeries or fusions, joint replacements, severe musculoskeletal or neurological diseases (e.g., ankylosing spondylitis, chronic destructive joint disease, multiple sclerosis, myodystrophies, neurodegenerative diseases), congenital deformities, acute herniated disc, medications affecting muscle elasticity, and pregnancy. Ethics approval obtained; written informed consent provided. Raters: Two sports science students trained in the procedures conducted all measurements. Measurement systems: Tape measure for Fingertip-to-Floor (FtF) and Lateral Inclination (LI); digital inclinometer (Acumar ACU002; integer readout, assumed absolute measurement error 0.3°) for Retroflexion of the trunk modified after Janda (RF), Shoulder test modified after Janda (ST), and modified Thomas test (TT). Tests primarily assess multi-joint trunk and proximal limb mobility. ROM tests: - FtF: active trunk/hip flexion; distance fingertip-to-floor (smaller is better). - LI (left/right): active lateral trunk flexion with back against wall; distance fingertip-to-floor. - RF: active spinal extension in prone with pelvis strapped; inclinometer on sternum. - ST (left/right): passive shoulder mobility; supine, shoulder abducted 90°, elbow extended; inclinometer on radius proximal to styloid. - TT (left/right): passive hip extension/extensibility; pelvic tilt standardized to 0° with inclinometer near ASIS; thigh inclination measured above patella. Procedure: No separate warm-up or familiarization; each repetition acts as specific warm-up. Each participant completed 20 repetitions of each test, order randomized. Each repetition held at maximal (active or passive per test) ROM for ~3 s; examiner counted down from 3 and recorded ROM at zero. Rest between repetitions: ~3 s. All tests completed in one day. Two raters recorded measures. Statistical analysis: Conducted in BiAS 11.08 and R (ggplot2 for figures). No formal power analysis due to pilot nature and unknown dispersion. At individual level, a regression was performed per participant to determine slope sign (ROM gain) and counts of individuals with positive gain were summarized. For group-level effects across 20 repetitions, repeated-measures ANOVA (if normal) or Friedman test (if non-normal) with multiple comparisons (Bonferroni corrected) assessed overall and within-session changes. Where sign test indicated positive trend, non-linear mixed-effects regression modeled the acute effect with a*exp(−b*x)+c (a amplitude at start, b rate parameter, c asymptote), including random effects for repeated measures. If the non-linear model was inadequate (non-significant parameter estimates), linear mixed-effects regression (a − x + b) quantified the trend. Alpha = 0.05. Measurement accuracy was summarized as the mean standard error of measurement across repetitions.

- Overall effects: Significant flexibility gains within 20 repetitions in 7/8 conditions: FtF p<0.001; LI-left p<0.001; LI-right p<0.001; RF p=0.009; ST-left p<0.001; ST-right p=0.003; TT-left p<0.001. TT-right showed no significant change (p=0.93). - Onset of significant within-session change: First significant ROM gain detected after approximately 5–8 repetitions for FtF, LI-left/right, RF, and ST-left; for ST-right after 19 repetitions; TT-left/right showed no significant pairwise changes despite overall test result for TT-left. - Individual-level ROM gain counts (positive slope): FtF 22/22; LI-left 18/22; LI-right 20/22; RF 16/22; ST-left 20/22; ST-right 19/22; TT-left 16/22; TT-right 13/22. - Measurement error (mean SEM) by side: LI-left/right 0.664/0.665; ST-left/right 1.650/1.989; TT-left/right 1.185/1.564. - Model fits: Non-linear mixed-effects regression indicated a repetition-dependent gradual decline in ROM gains (plateau formation) for FtF, RF, LI-left/right, ST-left, and TT-left. For ST-right and TT-right, the non-linear model was inadequate; linear mixed-effects regression showed a positive slope for ST-right (slope of at least 0.127 of parameter 'a') and no significant slope for TT-right. - Magnitude of increase: Across tests, total ROM increases were approximately 1–6 degrees (inclinometer-based tests) or 2–6 cm (tape measure tests). Plateau (e.g., ~80% of total ROM increase) typically occurred between ~10th and 13th repetition for FtF, LI-left/right, ST-left, and TT-left; RF reached plateau earlier (~5th repetition), potentially reflecting fatigue or different tissue constraints. - Practical counts from regression: Similar repetition counts across tests to reach given proportions of maximal ROM gain (e.g., moving from 50% to 60% typically required 1–2 additional repetitions; approaching 80–90% could require up to ~5 more repetitions).

Findings support the hypothesis that common ROM tests elicit an acute, repetition-dependent stretching effect analogous to that observed in stretching exercises: large early gains followed by diminishing improvements and eventual plateau. The non-linear regression in six of eight conditions characterized this behavior, allowing estimation of repetitions required to reach portions of the maximal within-session ROM increase. Practically, assessing ROM in the plateau region can improve standardization when participants have unknown or varying warm-up states; however, even near the plateau, small gains may still occur. Differences among tests likely reflect biomechanics and loading: FtF and LI (tape measure) showed consistent gains and low measurement error; inclinometer-based tests had coarser resolution (integer degrees) and higher measurement variability. Active tests (FtF, LI, RF) were performed at maximal torque, whereas passive tests (ST, TT) relied on gravity with sub-maximal torque; such differences can yield distinct dose–response behaviors. RF reached plateau earlier, potentially due to fatigue from repeated maximum elbow extension and the ligamentous limitations of spinal extension (e.g., ligamentum longitudinale anterius). Contralateral discrepancies for ST and TT (right sides showing higher measurement error and less consistent patterns) may be influenced by handedness/footedness distribution and procedural nuances. Dose (hold time) differences compared to stretching literature may account for later plateau formation in this study (3 s holds per repetition vs longer static stretching durations). Given that within-session ROM changes are measurable and non-linear, ROM values obtained using protocols with differing repetition counts, warm-ups, or averaging should not be directly compared. The presented functions and repetition guidance support selecting repetition counts that place measurements near a stable plateau, enhancing comparability across assessments in young healthy adults.

Most ROM tests demonstrated an acute, repetition-dependent increase in ROM characterized by diminishing gains and plateau formation; achieving 0–50% of the total ROM increase required approximately as many repetitions as moving from 50–75%. Non-linear regression modeled this behavior for most tests, indicating that the acute effect known from stretching also applies to typical ROM assessments. Practitioners and researchers should standardize repetition counts and consider measuring near the plateau to improve reliability and comparability when assessing young healthy adults.

- Pilot study with small sample (n=22) of young healthy sports students; findings may not generalize to elderly or clinical populations. - No formal power analysis; effect sizes and variability were unknown a priori. - Measurement resolution limitations: digital inclinometer recorded integer degrees, increasing measurement error relative to tape measurement. - Within-session protocol only; no between-day reliability assessed. No separate warm-up or familiarization, and only ~3 s holds per repetition. - Potential fatigue effects, especially in RF due to repeated maximal effort and elbow extension. - Contralateral inconsistencies (ST and TT right sides) and higher measurement error may be influenced by handedness/footedness and procedural differences. - Short inter-repetition rest (~3 s) may influence performance. - The plateau definition is descriptive; small gains persisted with higher repetitions, complicating precise plateau identification.