Intended for Healthcare Professionals
You are here
Home > Blog > Family Practice Medicine > Powerful Muscles In Bariatric Patients: A Fracture Risk Assessment

Powerful Muscles In Bariatric Patients: A Fracture Risk Assessment

Powerful Muscles In Bariatric Patients: A Fracture Risk Assessment


In this investigation, the primary objective was to assess the consistency of test results measuring lower limb muscle strength and rate of torque development (RTD) utilizing isokinetic dynamometry in adults grappling with obesity, defined as individuals with a body mass index (BMI) equal to or exceeding 35 kg/m^2.


Thirty-two adults, with an average BMI of 43.8 ± 6.6 kg/m^2, who were potential candidates for bariatric surgery, were recruited for the study. Over the course of three separate test sessions, spaced apart by intervals of 3 to 7 days, isokinetic and isometric knee extensor (KE) and flexor (KF) strength were evaluated using an isokinetic dynamometer (Biodex 4).


The outcomes revealed no statistically significant disparities in peak KE and KF torque across the various test modalities between the sessions. Intra class correlation (ICC) coefficients ranged from 0.91 to 0.94 between the initial and second sessions, and from 0.94 to 0.97 between the second and third sessions. The standard error of measurement (SEM%) and coefficient of variation (CV) exhibited ranges from 4.3% to 7.3% across the test sessions.


Moreover, the assessment of KE RTD exhibited notable reliability across successive test sessions post-familiarization, with ICC, CV, and SEM% values ranging from 0.84 to 0.90, 13.3% to 20.3%, and 14.6% to 24.9%, respectively. These findings underscore the robustness of utilizing isokinetic dynamometry in assessing lower limb muscle strength and RTD in adults with obesity, offering valuable insights for clinical and research endeavors in this population.



Bariatric surgery stands as a potent intervention for managing obesity in adults, thereby mitigating the risk of associated ailments and decreasing overall mortality rates. However, a notable drawback of this procedure includes the common occurrence of postoperative declines in skeletal muscle mass and strength. Studies have shown significant reductions in appendicular lean muscle mass by 18%-19% and maximal isokinetic and isometric lower limb muscle strength by 16%-34% following surgery. Consequently, the development of effective intervention strategies to preserve muscle mass and strength in this demographic is imperative.


Accurate evaluation of maximal muscle strength, including rapid force capacity, is pivotal in assessing intervention protocols or disuse effects. Various statistical methods can be employed to assess the reliability of physical tests, encompassing evaluations of agreement between repeated measurements, measurement error, and systematic changes in mean values between successive test sessions. Learning effects, indicative of improvements due to repeated testing, can confound the assessment of muscle strength changes over time, necessitating meticulous consideration of familiarization procedures to minimize their influence.


Isokinetic dynamometry represents the gold standard for assessing maximal muscle strength in the lower limbs. While prior studies have demonstrated good-to-excellent reliability of isokinetic dynamometry in healthy adults and clinical populations, potential learning effects have been observed, necessitating evaluation in specific clinical contexts such as adults eligible for bariatric surgery or those with obesity.


Rate of torque development (RTD) serves as a crucial metric for assessing rapid muscle force capacity, particularly in tasks characterized by short contraction times. Monitoring changes in RTD may prove valuable in individuals undergoing bariatric surgery, given their heightened fracture risk. While the test-retest reliability of RTD has been established in healthy populations, it remains unexplored in adults with obesity.

The principal objective of this study was to assess the intersession test-retest reliability of lower limb isokinetic muscle strength and RTD assessments in adults eligible for bariatric surgery. Specifically, the study aimed to determine whether separate familiarization sessions could mitigate potential learning effects and enhance reliability.



Inclusion Criteria


  1. Body Mass Index (BMI): Participants were required to have a BMI equal to or greater than 50 kg/m^2, or a BMI of 35 kg/m^2 or higher coupled with an obesity-related comorbid condition. Such comorbidities included type 2 diabetes, sleep apnea, arthrosis of the hip or knee, polycystic ovary syndrome, or treatment-resistant hypertension.


  1. Recruitment Source: Participants were recruited from a patient pool referred to The South Danish Obesity Initiative (SDOI) at the University Hospital of Southern Denmark, Esbjerg, or through social media postings.


  1. Health Screening: Prior to inclusion, candidates underwent screening for obesity-related comorbidities and potential risks associated with participation. Those with contraindications for muscle testing, such as recent knee or hip arthroplasty, postsurgery complications, or severely limited range of motion (ROM), were excluded from the study.


  1. Ethical Approval: The study was conducted in accordance with the Declaration of Helsinki, and approval was obtained from The Regional Committees on Health Research Ethics for Southern Denmark. Participants provided written informed consent before inclusion in the study.


Exclusion Criteria

  1. Contradictions for Muscle Testing: Individuals with recent knee or hip arthroplasty, post surgery complications, or severely limited range of motion (ROM) were excluded from the study due to potential risks associated with muscle testing.


  1. Systolic Blood Pressure: Participants with systolic blood pressure exceeding 180 mmHg upon arrival at the laboratory were excluded from testing, as elevated blood pressure could pose a risk during physical assessments.


Overall, the study recruited adults with severe obesity, ensuring inclusion of individuals with diverse obesity-related comorbidities while excluding those with contraindications for muscle testing or elevated blood pressure levels, thereby prioritizing participant safety and research integrity.



The data were expressed as means and standard deviations (SD). Prior to statistical analysis, normality of the data distribution was assessed using quantile-quantile (Q-Q) plots. In instances where the data deviated from a Gaussian distribution, nonparametric testing methods were employed.


To ascertain whether there existed a systematic change in group means between test sessions, indicative of either a learning effect or accumulative fatigue from the test procedures, a repeated-measures analysis of variance was conducted.


Intraclass correlations (ICC1.1) with 95% confidence intervals (95% CI) were utilized to assess the agreement between successive measurements. The ICC values were interpreted as follows: less than 0.5 denoting poor agreement, 0.5 to 0.75 indicating moderate agreement, 0.75 to 0.90 suggesting good agreement, and greater than 0.90 signifying excellent agreement.

Further evaluation of test reproducibility was conducted through the calculation of within-subject coefficient of variation (CVW-S). CVW-S was computed by dividing the standard deviation (SD) by the grand mean, with SD derived using the formula: SD = √(∑(d^2)/2n), where ‘d’ represents the test-retest difference.


Measurement error was quantified using the standard error of measurement (SEM) and SEM%. SEM was determined using the formula: SD × √(1−ICC). SEM% was obtained by dividing SEM by the grand mean.


The smallest detectable difference (SDD) was calculated to establish the threshold for the smallest detectable change at the individual level, expressed in both absolute and relative units, utilizing the formula: SDD = 1.96 × √(2 × SEM).


Statistical significance was set at a p-value of 0.05 or less for two-tailed testing, ensuring robust evaluation of the reliability and reproducibility of the measured parameters.



Initially, 495 current or former patients from the South Danish Obesity Initiative (SDOI) patient cohort were screened, with 253 meeting the primary inclusion criterion of BMI≥35 kg/m^2. Subsequently, 37 potential participants expressed their willingness to partake, of which 26 were enrolled after screening for obesity-related comorbidities and potential risks associated with the study. Additionally, seven participants meeting the inclusion criteria were recruited via social media. One participant withdrew consent due to transient severe muscle soreness post the first test session. Ultimately, data from 32 participants were included for final analysis.


The participants had a mean age of 49.9 ± 7.8 years and a BMI of 43.8 ± 6.6 kg/m^2. A majority were females (81%), with 78% presenting at least one obesity-related comorbidity, notably arthrosis in the hip or lower extremities (47%) and sleep apnea (38%).


Regarding reliability statistics for knee extensor (KE) and flexor (KF) peak torque, no significant differences were observed between test sessions. Intraclass correlation coefficients (ICC) for both isokinetic and isometric KE peak torque ranged from 0.93 to 0.98, with coefficients of variation (CV) and standard error of measurement percentages (SEM%) below 7.5%. Similar trends were observed for KF peak torque, with ICC values ranging between 0.92 and 0.94 and CV and SEM% below 7.5% across all test sessions.


For rate of torque development (RTD) assessments, no significant differences were noted across the three sessions for any time intervals. ICC values for KE RTD ranged from 0.71 to 0.90, with improvements observed in sessions 2-3 compared to sessions 1-2. Reliability parameters, including CV, SEM%, and smallest detectable differences (SDD%), were generally better for late-phase RTD (0-100 and 0-200 ms) compared to early-phase RTD (0-30 and 0-50 ms). However, for KF RTD, reliability parameters were comparatively weaker, particularly for early-phase RTD intervals, although improvements were observed in session 2-3 for late-phase RTD (0-200 ms).


Overall, the study findings suggest robust test-retest reliability for both peak torque and RTD assessments, particularly in late-phase RTD intervals, highlighting the utility of isokinetic dynamometry in evaluating muscle strength and rapid force capacity in adults eligible for bariatric surgery.


In adults eligible for bariatric surgery, maximal dynamic and isometric muscle strength assessment of knee extensors (KEs) and flexors (KFs) using isokinetic dynamometry exhibited excellent test-retest reliability. This was evidenced by high intraclass correlation coefficient (ICC) values ranging from 0.92 to 0.98, indicative of strong agreement between repeated measurements. Moreover, small measurement errors ranging from 4.0% to 6.9% and low coefficients of variation (CV) below 10% further underscored the reliability of the assessments. Notably, including a separate familiarization session marginally improved reliability, measurement error, and CV, albeit to a slight extent.


Thus, isokinetic dynamometry emerges as a reliable tool for detecting even subtle temporal changes in lower limb muscle strength among adults with obesity, irrespective of the inclusion of a familiarization session. However, when it comes to assessing rapid force capacity (RTD), the intersession reliability was comparatively lower than for peak torque. Acceptable reliability for KE RTD, but not for KF RTD, was achieved only when preceded by a separate familiarization session. This underscores the importance of familiarization procedures in optimizing the reliability of RTD assessments, particularly for knee extensors.


Oncology Related Tools


Latest Research


About Author

Similar Articles

Leave a Reply