Training intensity quantification of core stability exercises based on a smartphone accelerometer

Balance assessment with smartphone devices in para-footballers with cerebral palsy

OBJECTIVES

To explore whether the mean lumbar acceleration is a feasible tool for determining minimum eligibility criteria to compete in cerebral palsy football, differentiating between new sports classes, and to assess the effect of foot contacts on balance evaluation and class distinction.

DESIGN

Cross-sectional study.

METHODS

A total of 146 male cerebral palsy footballers classified into FT1 (n=34), FT2 (n=87), and FT3 (n=25), alongside 12 non-impaired athletes as a control group, participated. Two trials of one-leg standing, performed with the more and less affected legs, were measured using a smartphone-based accelerometer.

RESULTS

Reliability was moderate-to-excellent (ICC3,1 > 0.70; SEM < 20 %). Significant differences were observed between legs for footballers with cerebral palsy but not for the control group. Mean lumbar acceleration and the number of foot contacts showed significant differences between footballers with cerebral palsy and controls, with pairwise comparisons revealing distinctions between classes. Receiver operating characteristic curves demonstrated high sensitivity and specificity for distinguishing the control group from FT3 using the most affected leg (1.00 [excellent]), with a cutoff score of 0.115 m/s2 achieving very high sensitivity and specificity.

CONCLUSIONS

Mean lumbar acceleration appears to be a suitable metric for assessing minimum impairment criteria for eligibility in para-sports for ambulant athletes with cerebral palsy. However, foot contacts during one-leg standing tests may mask true balance performance in individuals with more severe impairments, which could affect class distinction.

Correlation Between Pain Intensity and Trunk Sway in Seated Posture Among Office Workers with Chronic Spinal Pain: A Pilot Field-Based Study

This pilot study examines the relationship between pain intensity and trunk sitting postural control in 10 office workers with chronic spinal pain, using field-based real-time inertial sensors. Pain intensity was assessed with the Numeric Pain Rating Scale (NPRS) before and after work across three non-consecutive workdays, while postural control was evaluated through estimated center of pressure (COP) displacements. Linear and nonlinear metrics, including sway range, velocity, the Hurst exponent, and sample entropy, were derived from the estimated COP time series. Pearson correlation coefficients (r) and corresponding p-values were used to analyze the relationship between pain intensity and postural control. Significant correlations, though limited to specific metrics, were found (r = -0.860 to 0.855; p < 0.05), suggesting that higher pain intensity may be correlated with reduced postural variability. These findings provide preliminary insights into the potential link between pain intensity and postural control. Understanding trunk posture dynamics could inform the development of targeted ergonomic interventions to reduce musculoskeletal stress and improve sitting comfort in office environments.

Effect of Body Position and Support Surface on the Postural Control Challenge During the Pallof Press Exercise: A Smartphone Accelerometer-Based Study

Background and objectives: Although different variations of the Pallof press exercise are commonly performed in sports and fitness settings to increase core stability, the intensity/difficulty of these variations is unknown and therefore it is difficult to control the training load and establish exercise progressions. This study aimed to compare and rank the postural control challenge imposed by five different isometric variations of the Pallof press exercise through a smartphone accelerometer placed on the participants' pelvis and to explore sex differences in the lumbopelvic postural control during the exercise performance. Materials and Methods: Twelve physically active participants completed two testing sessions in which they performed two sets of five different isometric variations of the Pallof press exercise (changing the body position and/or the support surface: kneeling on a foam pad, feet together standing on the floor, tandem stance on the floor, feet together standing on a hemisphere ball, and tandem stance on a hemisphere ball). After confirming the acceleration data reliability (intraclass correlation coefficients ≥ 0.72 and typical errors ≤ 17%), a repeated measure ANOVA was carried out to classify the Pallof press variations according to the postural control challenge imposed on the participants and to analyze sex differences on postural control. Results: Significant effects were found for the within-subject factor exercise variations but not for the between-subject factor sex. Pairwise comparisons showed that the exercise variations performed on the hemisphere ball (feet together standing: 0.55 m/s2; tandem stance: 0.61 m/s2) imposed higher postural control demands than those performed on the other surfaces (kneeling on a foam pad: 0.17 m/s2; feet together standing on the floor: 0.22 m/s2; tandem stance on the floor: 0.31 m/s2). In addition, the tandem stance on the floor produced higher lumbopelvic accelerations than the Pallof press kneeling variation. Conclusions: The Pallof press performance in standing rather than kneeling (i.e., reducing the base of support and raising the center of gravity and the height of the lateral force applied by the elastic band) and on a hemisphere ball increased the exercise difficulty compared to more stable surfaces. This information could help to modulate the difficulty and establish progressions for this exercise in physically active young males and females.

Exercise Intensity Progressions and Criteria to Prescribe Core Stability Exercises in Young Physically Active Men: A Smartphone Accelerometer-Based Study

ABSTRACT

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.

Trunk muscle activation in prone plank exercises with different body tilts

BACKGROUND

Body tilt changes could affect the intensity/difficulty of core stability exercises, but there is still a lack of knowledge about its impact.

OBJECTIVE

To analyse the trunk muscles activation during prone plank exercises at different body tilts.

METHODS

Twenty-four young adults who performed recreational gymnastic activities participated in this study. Electromyography activity of the rectus abdominis (RA), external oblique (EO), internal oblique (IO) and erector spinae (ES) was recorded during the performance of six variations of the prone plank exercise (planking with feet supported on the ground [conventional horizontal position] and planking with feet supported on wall bars at five different heights increasing the angle tilt) and an inverted position exercise.

RESULTS

The RA, EO and IO activation in all prone plank variations were higher than those observed in the conventional prone plank. In addition, the coefficient of variation of the muscle activation increased with the declination angle, reaching the highest values in the inverted position for the RA and ES muscles.

CONCLUSION

The results seem to indicate that the body tilt variation could be used as an easy and inexpensive strategy for modulating the neuromuscular demands and the motor control challenge during planking exercises.

Smartphone accelerometry for quantifying core stability and developing exercise training progressions in people with multiple sclerosis

BACKGROUND

Core stability exercise programs have become popular in recent years for preserving balance and functional independence in people with multiple sclerosis (PwMS); however, their real impact is not well-known as the main intervention target (i.e., core stability) theoretically responsible for balance or functional improvements is not measured. The objective of this study was to test the reliability of accelerometers integrated into smartphones for quantifying core stability and developing exercise progressions in PwMS.

METHODS

Twenty participants with MS [age: 47.5±8.0 years; height: 1.62±0.07 m; mass: 63.4±10.9 kg; EDSS: 3.0 (1.5-6)] participated voluntarily in this study. CS was assessed in different variations of the front, side, and back bridges and bird-dog exercises by measuring the mean lumbopelvic acceleration in two testing sessions, separated by one week. Relative and absolute reliability of lumbopelvic acceleration of those exercise variations performed by more than 60% of the participants was analyzed by the intraclass correlation coefficient (ICC_3,1), and the standard error of measurement (SEM) and the minimal detectable change (MDC), respectively. Repeated measures ANOVAs were performed to detect a potential learning effect between test-retest assessments. Statistical significance was set at p < 0.05.

RESULTS

Reliability analyses revealed that good to excellent relative and absolute scores (0.85<ICC<0.96; 7.8%≤SEM≤19.2%; 21.6%≤MDC≤53.2%) for the mean lumbopelvic acceleration obtained during 10 of the 12 CS exercise variations performed by more than 60% of the participants. A non-significant between-session learning effect was detected in all the variables considered (all p values >0.05).

CONCLUSION

Smartphone accelerometry seems a low cost, portable and easy-to-use tool to objectively and reliably track core stability changes in PwMS through. However, in spite of the popularity of bridging and bird-dog exercises, only the short and long bridges and the three-point bird-dog positions proved feasible for most participants. Overall, this study provides useful information to evaluate and guide the prescription of core stability exercise programs in PwMS with mild-to-moderate impairment.

Short-term effects of lumbopelvic complex stability training in elite female road cyclists

OBJECTIVES

The purpose of this study was to determine the effects of short-term lumbopelvic stability training on muscular endurance and stability in elite female cyclists.

METHODS

Twenty-four female road cyclists were randomly allocated to a core training group (CTG, n=12) or control group (CG, n=12). In addition to their scheduled training the CTG performed a core training program, that consisted of 6 core exercises performed in a session every other day until a total of 8 training sessions were completed. The CG did not receive the core training program and completed their scheduled training. The lumbopelvic-hip complex was assessed pre- and post-core program included the following exercises: single leg deadlift (SLD), bird-dog (BD), plank test (PT), and side-bridge plank test (SPT).

RESULTS

In comparison to CG, CTG significantly improved the time to failure in PT, SPT-Left, and SPT-Right (p<0.05). Further, CTG resulted in a significant decrease in SLD (p<0.05) compared to CG for the three accelerometry measures.

CONCLUSION

The present results indicate that following 8 sessions of lumbopelvic stability training muscular endurance and core stability were enhanced.

Observational Screening Guidelines and Smartphone Accelerometer Thresholds to Establish the Intensity of Some of the Most Popular Core Stability Exercises

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.

Effects of a Specific Core Stability Program on the Sprint and Change-of-Direction Maneuverability Performance in Youth, Male Soccer Players

Although it is recommended to use sport-specific training programs to optimize performance, studies analyzing the effects of the core stability training with high levels of sport-specificity on athletic performance are insufficient and unclear. The objective of this study was to analyze the effects of the level of specificity of a CORE stability program on specific soccer actions. Fourteen youth players were randomly assigned to the specific core stability group (SCS; n = 7) or the general core stability group (GCS; n = 7). The eight-week intervention consisted of two weekly training sessions added to the usual soccer training. Both groups performed four CORE stability tasks. The SCS group followed the principle of sports specificity, while the GCS group performed CORE stability commons. Ten-meter linear sprinting (Sprint) and change-of-direction maneuverability (V-cut) were evaluated before and after the intervention programs. A statistically significant improvement was obtained in Sprint (d = 0.84 95% CI (0.22, 1.45), p = 0.008) and V-cut (d = 1.24 95% CI (0.52, 1.93), p < 0.001). At posttest, statistically nonsignificant differences were obtained between groups in Sprint (d = 1.03 95% CI (−0.25, 2.30), p = 0.082) and V-cut (d = −0.56 95% CI (−1.89, 0.78), p = 0.370). In conclusion, sprint and change-of-direction maneuverability were improved, but there was no superiority of any type of training.

Are Core Stability Tests Related to Single Leg Squat Performance in Active Females?

Core stability (CS) deficits can have a significant impact on lower limb function. The aim of this study was to investigate the relationship between two dynamic core exercise assessments and dynamic knee valgus during single-leg squats. In total, 20 physically active female students participated in this study. The OCTOcore smartphone application assesses CS during two dynamic exercise tests, the partial range single-leg deadlift (SLD) test and the bird-dog (BD) test. A two-dimensional assessment of a single-leg squat test was used to quantify participants’ hip frontal angle (HFA_SLS) and knee frontal plane projection angle (FPPA_SLS). Ankle dorsiflexion was evaluated through the weight-bearing dorsiflexion test. The correlational analyses indicated that the HFA_SLS was significantly related to the partial range single-leg deadlift test (r = 0.314, p < 0.05) and ankle dorsiflexion (r = 0.322, p < 0.05). The results showed a significant difference (p < 0.05) in the CS test between cases categorised as dynamic knee valgus (>10°) and normal (≤10°). The CS deficit may influence the neuromuscular control of the lumbopelvic-hip complex during single-leg movements. The link between CS and kinematic factors related to knee injuries was only observed when CS was measured in the SLD test but not in the BD test.

Changes in the Trunk and Lower Extremity Kinematics Due to Fatigue Can Predispose to Chronic Injuries in Cycling

Kinematic analysis of the cycling position is a determining factor in injury prevention and optimal performance. Fatigue caused by high volume training can alter the kinematics of the lower body and spinal structures, thus increasing the risk of chronic injury. However, very few studies have established relationships between fatigue and postural change, being these in 2D analysis or incremental intensity protocols. Therefore, this study aimed to perform a 3D kinematic analysis of pedaling technique in a stable power fatigue protocol 23 amateur cyclists (28.3 ± 8.4 years) participated in this study. For this purpose, 3D kinematics in hip, knee, ankle, and lumbar joints, and thorax and pelvis were collected at three separate times during the protocol. Kinematic differences at the beginning, middle, and end of the protocol were analyzed for all joints using one-dimensional statistical parametric mapping. Significant differences (p < 0.05) were found in all the joints studied, but not all of them occur in the same planes or the same phase of the cycle. Some of the changes produced, such as greater lumbar and thoracic flexion, greater thoracic and pelvic tilt, or greater hip adduction, could lead to chronic knee and lumbar injuries. Therefore, bike fitting protocols should be carried out in fatigue situations to detect risk factor situations.

Influence of the Amount of Instability on the Leg Muscle Activity During a Loaded Free Barbell Half-Squat

This study aimed to understand the acute responses on the muscular activity of primary movers during the execution of a half-squat under different unstable devices. Fourteen male and female high-standard track and field athletes were voluntarily recruited. A repeated measures design was used to establish the differences between muscle activity of the primary movers, the body centre of mass acceleration and the OMNI-Perceived Exertion Scale for Resistance Exercise (OMNI-Res) in a half-squat under four different stability conditions (floor, foam, BOSU-up and BOSU-down). A significant correlation was found between the highest performance limb muscle activity and body centre of mass acceleration for half-squat floor (r = 0.446, p = 0.003), foam (r = 0.322, p = 0.038), BOSU-up (r = 0.500, p = 0.001), and BOSU-down (r = 0.495, p = 0.001) exercises. For the exercise condition, the half-squat BOSU-up and BOSU-down significantly increased the muscle activity compared to half-squat floor (vastus medialis: p = 0.020, d = 0.56; vastus lateralis: p = 0.006, d = 0.75; biceps femoris: p = 0.000–0.006, d = 1.23–1.00) and half-squat foam (vastus medialis: p = 0.005–0.006, d = 0.60–1.00; vastus lateralis: p = 0.014, d = 0.67; biceps femoris: p = 0.002, d = 1.00) activities. This study contributes to improving the understanding of instability training, providing data about the acute muscular responses that an athlete experiences under varied stability conditions. The perturbation offered by the two BOSU conditions was revealed as the most demanding for the sample of athletes, followed by foam and floor executions.

Sempere Á, Vera-Garcia FJ, Barbado D. Understanding the Deterioration of Gait, Postural Control, Lower Limb Strength and Perceived Fatigue Across the Disability Spectrum of People with Multiple Sclerosis

Disability progression is a prominent feature of multiple sclerosis (MS). However, little is known about the extent to which physical condition parameters and perceived fatigue evolve during the disease. We analyzed how strength, balance, core stability and perceived fatigue differ among different cohorts of people with MS (PwMS) with different disability degrees and how these contribute to patients' gait speed and functional mobility. Sixty-three PwMS divided into three groups according to the "Expanded Disability Status Scale" (MS1: EDSS ≤ 1.5; MS2: 2 ≤ EDSS ≤ 3.5; MS3: 4 ≤ EDSS ≤ 6) and 22 healthy controls (HC) participated in this study. MS1 showed lower balance and hip strength compared to HC. MS2 showed lower balance, core stability, gait speed, and functional mobility than MS1. MS3 showed lower gait speed, functional mobility, balance, and knee flexion strength than MS2. No between-group differences were observed in perceived fatigue. Relative weight analysis showed that strength, balance and core stability explained 60%-70% of the variance in gait speed and functional mobility. The decline of each parameter did not evolve at the same rate across the different stages of the disease, being knee flexion strength and balance the most influential factors in the disability progression. Overall, these results provide useful information to guide exercise prescription at different stages of MS.

Inter-Rater Reliability, Concurrent Validity and Sensitivity of Current Methods to Assess Trunk Function in Boccia Player with Cerebral Palsy

Trunk function is a core factor to allocate Boccia players with cerebral palsy in BC1 and BC2 sport classes, according to the Boccia International Sports Federation (BISFed). However, the appropriateness of the current test to assess trunk function has never been studied to determine its reliability, validity and sensitivity to discriminate between different levels of impairment. Thirty-six players (BC1 = 13 and BC2 = 23) took part in this study. Trunk control was assessed through the BISFed trunk function scale (TFS) and a posturographic test battery consisting of two static and three dynamic tasks. The inter-rater reliability for the BISFed TFS was set at 94.44% of agreement. Moderate-to-high correlations were obtained between posturographic tasks (0.39 < r < 0.96; p < 0.05–0.01), while the BISFed TFS only correlated with two of the dynamic tasks and the overall dynamic score (−0.38 < r < −0.51; p < 0.05). The BISFed TFS was not able to discriminate between sport classes, whereas the static posturographic task did so (p = 0.004). Even though the current BISFed TFS presented good inter-rater reliability, it does not seem to have enough sensitivity to discriminate between BC1 and BC2. Although the static posturographic tasks were able to discriminate between sports classes, it seems necessary to develop new field tests assessing participants’ trunk stabilization abilities.

Progressions of core stabilization exercises based on postural control challenge assessment

PURPOSE

The intensity progression of core stabilization exercises (CSEs) is usually based on personal criteria rather than on objective parameters. To develop exercise progressions for four of the most common CSEs based on the postural control challenge imposed on the participants, and to analyze the effect of participants' sex and postural control level on these progressions.

METHODS

Seventy-six males and females performed five variations of front bridge, back bridge, side bridge and bird-dog exercises on two force platforms. The mean velocity of the center of pressure displacement was calculated to assess exercise intensity through the measurement of the participants' body sway (PBS).

RESULTS

In general, long bridges produced higher PBS than short bridges, bridging with single leg support produced higher PBS than bridging with double leg support and bridging on a hemisphere ball produced higher PBS than bridging on the floor. The most difficult bridging variations were those performed on a hemisphere ball with single leg support. Regarding the bird-dog, two-point positions produced higher PBS than three-point positions and the positions performed on a hemisphere ball produced higher PBS than those performed on the floor.

CONCLUSION

The CSE progressions obtained by males and females were very similar. However, the participants with high trunk control showed less significant differences between exercise variations than the participants with low trunk control, which shows the need to individualize the progressions according to the participants' training level. Overall, this study provides useful information to guide the prescription of CSE progressions in young physically active individuals.

Test-retest reliability of a smartphone app for measuring core stability for two dynamic exercises

Background

Recently, there has been growing interest in using smartphone applications to assess gait speed and quantify isometric core stability exercise intensity. The purpose of this study was to investigate the between-session reliability and minimal detectable change of a smartphone app for two dynamic exercise tests of the lumbopelvic complex.

Methods

Thirty-three healthy young and active students (age: 22.3 ± 5.9 years, body weight: 66.9 ± 11.3 kg, height: 167.8 ± 10.3 cm) participated in this study. Intraclass correlation coefficient (ICC), coefficient of variation (%CV), and Bland–Altman plots were used to verify the reliability of the test. The standard error of measurement (SEM) and the minimum detectable difference (MDD) were calculated for clinical applicability.

Results

The ICCs ranged from 0.73 to 0.96, with low variation (0.9% to 4.8%) between days of assessments. The Bland–Altman plots and one-sample t-tests (p > 0.05) indicated that no dynamic exercise tests changed systematically. Our analyses showed that SEM 0.6 to 1.5 mm/s-2) and MDD (2.1 to 3.5 mm/s-2).

Conclusion

The OCTOcore app is a reliable tool to assess core stability for two dynamic exercises. A minimal change of 3.5 mm/s-2 is needed to be confident that the change is not a measurement error between two sessions.