The side bridge test (SBT) is one of the most popular tests to assess isometric trunk lateral flexor endurance. The aim of this study was to assess the validity and reliability of the SBT in healthy females. Twenty-four (24.58 ± 3.92 years) physically active (1–2 h of moderate physical activity, 2–3 times a week) females voluntarily participated in this study. The surface electromyography (EMG) of eight abdominal, back, shoulder and hip muscles was measured during the SBT. Normalized median frequency slopes (NMF_slope) were calculated to analyze the muscle fatigue. The EMG amplitudes were normalized to maximum EMG values to assess muscle activity intensity. A one-week test-retest design was performed to evaluate the SBT reliability through the ICC_3,1 and typical error. Higher NMF_slopes and normalized EMG amplitudes were found in deltoids, abdominal obliques, rectus abdominis, and erector spinae in comparison to latissimus dorsi, gluteus medius, and rectus femoris. However, no significant differences were found between the trunk lateral flexors and the deltoids. Linear regression analysis showed that SBT performance could be significantly predicted by external oblique and deltoid NMF_slope (adjusted R² = 0.673) and by body mass and trunk height (adjusted R² = 0.223). Consistency analysis showed a high intraclass correlation coefficient (0.81) and a relatively high typical error (10.95 s). Despite the good relative reliability of the SBT, its absolute reliability was low and its validity questionable, as the shoulder muscle activation and fatigue and the individuals’ anthropometric characteristics played an important role in SBT performance.

Objectives: Determine if (a) a better trunk stability and endurance are associated with an improved whole‐body dynamic balance, and if (b) the assessment tests can be interchanged within each capability.Methods: Sixty‐three physically active young males performed three trunk stability (i.e., the lumbopelvic stability, the unstable sitting and the sudden loading sitting tests), three trunk muscle endurance (i.e., the Biering–Sørensen, the side bridge and the front bridge tests) and four whole‐body dynamic balance (i.e., the tandem and the single‐leg stance, the Y‐Balance, and the single‐leg triple hop tests) tests two times. After assessing the reliability of the variables, a Pearson correlation analysis was performed.Results: The correlations between trunk stability and endurance tests with dynamic balance tests were non‐significant except for the unstable sitting test with both the tandem (r = 0.502) and the single‐leg stance (r = 0.522) tests. Moreover, no relationships were observed between the trunk stability and the trunk muscle endurance tests. Interestingly, no relationships were found between most tests within each capability (i.e., trunk stability, trunk endurance, and dynamic balance) except: (i) the front bridge stability test and the back (r = 0.461) and the side (r = 0.499) bridge stability tests; (ii) the two side bridge endurance tests (r = 0.786); (iii) the tandem and the single‐leg stance tests (0.439 ≤ r ≤ 0.463); (iv) the Y‐Balance and the single‐leg triple hop tests (0.446 ≤ r ≤ 0.477).Conclusion: Better trunk function does not seem to be a relevant factor for dynamic balance in young active males. In this population, specific measures are needed as the test interchangeability is questioned.

The lack of training load control, mainly exercise intensity, is one of the main limitations of core stability (CS) programs, which makes the training individualization and the analysis of the dose-response relationship difficult. The objectives of this study were to assess the inter-and intra-rater agreement when using new observational screening guidelines to decide if a core stability exercise represents an adequate training intensity level for a given participant. Besides, the relationship between experts' ratings based on these criteria and pelvic accelerations recorded with a smartphone accelerometer was also analyzed. Ten healthy physically active participants with a smartphone accelerometer placed on their pelvis were video-taped while performing a progression of seven variations of the front bridge, back bridge, side bridge and bird-dog exercises. Two expert and four non-expert raters watched the videos and used the observational screening guidelines to decide for each exercise variation if it represented an adequate training intensity level or not. In order to analyze the inter-and intra-rater agreement, several Kappa (κ) statistics were used. Receiver operating characteristic (ROC) curves to explore if the accelerometry allowed to establish pelvic acceleration thresholds representing the minimum level of exercise intensity for CS training. Cut-off acceleration values were calculated balancing sensitivity (Se) and 1-specifity (1-Sp) indexes (i.e., Youden index) or minimizing 1-Sp. The intra-and inter-rater analysis showed a substantial-high level of agreement with a prevalence-adjusted bias-adjusted Kappa > 0.69. The ROC curves showed that the acceleration thresholds for the bridging exercises were very similar, with global cut-off values of 0.35 m/s² (Se = 82%; 1-Sp = 15%) when using the Youden Index and of 0.50 m/s² when minimizing 1-Sp (Se = 31%), whilst the bird-dog exercise showed lower cut-off values (Youden Index: 0.21 m/s², Se = 90%, 1-Sp = 16%; minimizing 1-Sp: 0.32 m/s², Se = 40%). Overall, this study provides observational screening guidelines and smartphone accelerometer thresholds to facilitate the decision-making process when setting the intensity of some of the most popular core stability exercises in young physically active individuals.

Heredia-Elvar, JR, Juan-Recio, C, Prat-Luri, A, Barbado, D, Ríos-Calonge, Jdl, and Vera-Garcia, FJ. Exercise intensity progressions and criteria to prescribe core stability exercises in young physically active men: a smartphone accelerometer-based study. J Strength Cond Res 38(2): 266–273, 2024—The establishment of core stability (CS) exercise intensity progressions in sport and clinical settings is normally based on subjective criteria. Therefore, this study aimed to develop exercise intensity progressions for some of the most common CS exercises through smartphone accelerometry and to analyze the effect of the subjects' lumbopelvic postural control on these progressions. Fifty-seven healthy young physically active male students performed 7 isometric variations of front bridge, back bridge, side bridge, and bird-dog exercises with a smartphone accelerometer placed on the pelvis. Mean pelvic accelerations were calculated during each variation to evaluate the lumbopelvic postural control challenge imposed on the subjects as an index of exercise intensity of difficulty. For the bridge exercises, long bridging produced higher pelvic accelerations than short bridging, bridging with single-leg support was more intense than bridging with double-leg support (even with both legs on a hemisphere ball for the back and front bridge), and the most difficult variations were those performed on a Swiss ball, mainly the variations with single-leg support. For the bird-dog exercise, the 2-point positions were more intense than the 3-point positions, the variations performed with a knee on the hemisphere ball produced higher pelvic accelerations than similar variations performed with the forearm on the hemisphere ball, and the variations with limb motions generated higher pelvic accelerations than similar variations performed without limb motions. Although the CS exercise progressions were very similar across subjects, our results showed the need to individualize the prescription of the CS exercise progressions based on the subjects' lumbopelvic postural control level.

An accurate trunk muscle strength assessment seems very important to design and individualize training and rehabilitation programs in clinical and sport settings. Hand-held dynamometers (HHDs) are interesting alternatives to isokinetic dynamometers for assessing trunk isometric muscle strength because they are inexpensive instruments and easy to use. This cross-sectional observational study aimed to examine the reliability of two novel sitting tests for assessing trunk flexion and extension isometric strength using an HHD and their relationship with two other novel isometric tests that use an isokinetic dynamometer. Twenty-four female amateur athletes (age: 24.5 ± 2.64 years; body height: 164.45 ± 6.33 cm; body mass: 63.17 ± 10.35 kg) participated in this study. A test-retest design was carried out one-week apart to examine the reliability. The relationship and the degree of agreement between the HHD and the isokinetic dynamometer measurements were analysed using Pearson correlation and Bland-Altman analysis, respectively. In general, the reliability of all isometric strength tests was good, with ICCs ranging from 0.65 to 0.87 and typical error < 15%. Pearson correlations were moderate, with values of r = 0.47 (R2 = 0.22) and r = 0.42 (R2 = 0.18) for flexion and extension strength, respectively. Bland-Altman plots showed no agreement between HHDs and isokinetic measurements. All trunk isometric tests using both, an isokinetic dynamometer and HHDs, provide reliable measurements for assessing trunk flexion and extension strength. According to the comparative analysis, both measurement types are different and cannot be used interchangeably. Health and sport professionals should choose the test that best suits the biomechanical characteristics required for functional goals or success in a given sport.

The Biering-Sorensen test (BST), the Side Bridge test (SBT) and the Ito test (IT) are three of the most used field-based tests to assess isometric trunk muscle endurance. The objectives were to analyze the relationship between the participants’ test performance and several anthropometry parameters, the data consistency and the sex effect on test scores. Forty-five recreational athletes (27 males and 18 females) performed the three isometric trunk holding tests twice in two testing sessions to perform the reliability analysis and later, the three tests were performed once more, but in different sessions (one for each test) to maximize test performance and reduce the bias of muscle fatigue. Data (i.e., test scores and anthropometric variables) were logarithmic transformed to ensure the normality and homoscedasticity assumption. Relative reliability was very good, with ICCs > 0.70 in all tests, while absolute reliability showed high values of typical error (12.1–24.1%). ANOVA showed significant differences between sessions for the BST and the SBT scores and between sexes in the BST (females: 193.7 ± 53.2 s; males: 161.9 ± 52.2 s). IT scores showed a negative correlation with mass in both sexes (males: r = −.436; p = .026; females: r = −.562; p = .019) and with biileocrestal breadth (r = −.735; p = .001) and biacromial breadth (r = −.745; p = .001) in females. BST scores correlated significantly with biacromial breadth (r = −.379; p = .050) in males. SBT scores were negatively correlated to mass (r = −.703; p < .001), biileocrestal breadth (r = −.672; p < .001), biacromial breadth (r = −.601; p = .001) and acromion-iliac index (r = −.493; p = .010) in males and to relative lower extremity length (r = −.493; p = .038) in females. In conclusion, trainers and clinicians should consider individual anthropometric and sex differences when interpreting test results, as larger body mass and upper body breadth may artificially lower endurance scores. Adjustments to normative values may be required in applied settings. Moreover, based on the reliability analysis, these tests could be used to classify participants consistently, but the BST and the SBT require an extensive familiarization period and they don’t seem to be useful to detect small changes in participants’ performance over time.