Phase angle, muscle tissue, and resistance training

Phase angle as a marker of muscle quality: A systematic review and meta-analysis

BACKGROUND & AIMS

Phase angle (PhA) is a biomarker derived from raw bioelectrical impedance analysis (BIA) values: resistance (R) and reactance (Xc). PhA reflects cellular membrane integrity and, as a result, has been considered a marker of fluid distribution, making it a potential prognostic indicator. A growing body of research demonstrates independent associations between PhA and muscle strength, mass, and composition. In this context, PhA has the extra potential to serve as a marker of muscle quality. However, the evidence supporting its use for this purpose is not well established. This study aimed to investigate the relationship between PhA and markers of muscle quality.

METHODS

This systematic review and meta-analysis (Internal Prospective Register of Systematic Reviews - PROSPERO on a registration code: CRD42024507853) focused on observational studies assessing the relationship between PhA and markers of both concepts of muscle quality: the muscle quality index (MQI: strength by a unit of mass) and the muscle composition (i.e., skeletal muscle radiodensity [SMD], muscle echogenicity, muscle fat fraction, inter- and intramuscular adiposity). Risk of bias was assessed using the Newcastle-Ottawa Scale (NOS) and Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2), while the certainty of evidence was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach. Meta-analyses with a random-effects model were conducted.

RESULTS

Seventeen studies were included in this systematic review, encompassing 2710 participants. Meta-analyses demonstrated that PhA had a moderate positive correlation coefficient with SMD (4 studies, 924 participants; r = 0.54, 95 % confidence interval (CI) 0.38 to 0.69, heterogeneity (I2) = 92 %) and good accuracy (85 %) for classifying low SMD (2 studies, 390 participants; Area Under the Curve - AUCpooled 0.85, 95 % CI 0.78 to 0.92, I2 = 0 %). PhA was inversely-moderately correlated with muscle echogenicity (8 studies, 1401 participants; r = - 0.42, 95 % CI - 0.57 to - 0.24, I2 = 82 %) and positively-weakly correlated with MQI (2 studies, 191 participants; r = 0.36, 95 % CI 0.21 to 0.49, I2 = 17 %). All studies had a higher risk of bias. The certainty of evidence ranged from low to very low.

CONCLUSION

Despite technical challenges, this study demonstrates the potential of PhA as a surrogate marker for muscle quality, particularly expressing muscle composition (SMD). Future studies should utilize BIA with standardized protocols to potentially establish specific cutoff values for PhA, thereby enhancing its diagnostic accuracy and clinical applicability. These studies could additionally explore the mechanisms underlying the associations between PhA and muscle quality aspects. In cases where technical factors are not easily controlled, the use of standardized PhA (SPhA), which converts PhA into Z-scores, could be beneficial. Although this warrants investigation, this approach (SPhA) has the potential to account for variables such as age, sex, device differences, and health status.

Use of phase angle as an indicator of overtraining in sport and physical training

The use of bioelectrical impedance analysis (BIA) is now well established in healthcare as an essential support tool for patient management in various clinical settings. Its use in sports is rapidly expanding due to the valuable insights it offers, helping to better structure athletes' diets and training programs, thereby optimizing their performance. In the context of sport, however, there is a consensus regarding the importance of proper interpretation of BIA-derived data, which cannot be limited to mere estimation of body composition. In this sense, therefore, the evaluation and interpretation of raw bioelectrical parameters, including resistance, reactance, and phase angle (PhA) is of relevant importance. The assessment of PhA is particularly significant in the context of sports, as it is closely linked to key factors such as muscle mass, strength, and overall muscle quality. However, the existing relationship between PhA and systemic, and loco-regional inflammation, which, in a broader sense, is the rationale behind its use for assessing and monitoring localised muscle damage. Thus, the importance of PhA monitoring during training becomes evident, as it plays a crucial role in assessing and potentially identifying functional impairments, such as overtraining syndrome, as well as muscle injury and related changes in fluid distribution, at an early stage. The aim of this review is to provide the scientific basis necessary to consider the use of whole-body PhA as an indicator of overtraining.

Raw bioelectrical data and physical performance in track and field athletes: Are there differences between the sexes in the relationship?

Objectives

The study aimed to investigate the relationship between raw bioelectrical data and physical performance in track and field athletes. Specifically, the objectives were to determine: 1) whether a regional bioelectrical impedance approach provides additional insights compared to whole-body analysis, 2) the reliability of the Levi Muscle Index (LMI) in this context, and 3) whether there are differences in these relationships between male and female athletes.

Design

This study utilized a cross-sectional design involving thirty-one female athletes (mean age 21.4 ± 3.8 years) and thirty male athletes (mean age 21.1 ± 2.6 years) from track and field. On a single day, participants underwent whole-body and regional bioelectrical impedance assessments focusing on the lower limbs, alongside strength and speed performance tests.

Results

The study found no significant differences in the relationship between whole-body versus regional bioelectrical impedance and performance tests. Resistance (R) demonstrated an inverse correlation, while phase angle (PhA) and Levi Muscle Index (LMI) showed direct correlations with most performance variables in track and field athletes. Significant differences were observed between male and female athletes across all parameters, with male athletes exhibiting superior performance, higher PhA and LMI values, and stronger correlation coefficients compared to females.

Conclusions

In summary, this study highlights the intricate relationship between body composition and physical performance in athletes. It underscores the importance of considering sex differences and the reliability of raw bioelectrical data, whether obtained through regional or whole-body approaches, in assessing athletic performance.

Resistance Training Using VAriable Resistance Suit (VARS) Increased Isometric and Isokinetic Muscle Strength

While resistance training promotes muscle hypertrophy and strength, accessibility of equipment is a barrier. This study evaluated a wearable VAriable Resistance Suit (VARS) as a novel and alternative method to achieve muscle strength improvement. It was hypothesized that by providing adjustable, bi-directional and speed dependent resistance, VARS can target specific muscles to improve muscle strength via an accessible and portable device. Twelve untrained healthy male adults (22.08 ± 4.1 years old) participated in an 8-week long resistance training using VARS to strengthen four muscles (biceps brachii, triceps brachii, biceps femoris, rectus femoris) of their non-dominant arm and leg using VARS. The results showed significant improvements in the muscle strength measured by isokinetic dynamometer - 49.9±9.6% increase in isokinetic force and 30.6±7.6% increase in isometric force. Muscle size and body composition were also assessed using ultrasound imaging and bioelectrical impedance analysis, which did not show significant changes. The study demonstrates the efficacy and feasibility of VARS as a resistance training tool to achieve muscle strength improvement and its potential extension to clinical populations.

Non invasive techniques for direct muscle quality assessment after exercise intervention in older adults: a systematic review

BACKGROUND

The aging process induces neural and morphological changes in the human musculoskeletal system, leading to a decline in muscle mass, strength and quality. These alterations, coupled with shifts in muscle metabolism, underscore the essential role of physical exercise in maintaining and improving muscle quality in older adults. Muscle quality's morphological domain encompasses direct assessments of muscle microscopic and macroscopic aspects of muscle architecture and composition. Various tools exist to estimate muscle quality, each with specific technical requirements. However, due to the heterogeneity in both the studied population and study methodologies, there is a gap in the establishment of reference standards to determine which are the non-invasive and direct tools to assess muscle quality after exercise interventions. Therefore, the purpose of this review is to obtain an overview of the non-invasive tools used to measure muscle quality directly after exercise interventions in healthy older adults, as well as to assess the effects of exercise on muscle quality.

MAIN TEXT

To address the imperative of understanding and optimizing muscle quality in aging individuals, this review provides an overview of non-invasive tools employed to measure muscle quality directly after exercise interventions in healthy older adults, along with an assessment of the effects of exercise on muscle quality.

RESULTS

Thirty four studies were included. Several methods of direct muscle quality assessment were identified. Notably, 2 studies harnessed CT, 20 utilized US, 9 employed MRI, 2 opted for TMG, 2 adopted myotonometry, and 1 incorporated BIA, with several studies employing multiple tests. Exploring interventions, 26 studies focus on resistance exercise, 4 on aerobic training, and 5 on concurrent training.

CONCLUSIONS

There is significant diversity in the methods of direct assessment of muscle quality, mainly using ultrasound and magnetic resonance imaging; and a consistent positive trend in exercise interventions, indicating their efficacy in improving or preserving muscle quality. However, the lack of standardized assessment criteria poses a challenge given the diversity within the studied population and variations in methodologies.. These data emphasize the need to standardize assessment criteria and underscore the potential benefits of exercise interventions aimed at optimizing muscle quality.

Body composition characteristics and influencing factors of different parts of sarcopenia in elderly people: A community-based cross-sectional survey

Objectives

This study aims to describe the differences in body composition among different body parts of the elderly in the community and its relationship with sarcopenia.

Methods

Elderly people aged ≥65 underwent bioelectric impedance analysis testing and were categorized into a sarcopenia group, possible sarcopenia group, and control group. The characteristics of body composition indicators in different parts and their relationship with different stages of sarcopenia were analyzed.

Results

The sarcopenia group illustrated the lowest values of FFM, FFM%, BFM, BFM%, ICW, and limb PhA, along with higher ECW/TBW in the trunk and left leg compared to the control group. The possible sarcopenia group showed lower FFM% in limbs and trunk, and higher BFM% compared to the control group. Gender differences in elderly body composition were observed, with an increase in BFM% in various body parts posing a risk factor for possible sarcopenia in elderly males, whereas an increase in BFM% except in the left arm was a protective factor for sarcopenia in elderly females.

Conclusion

The body composition of the elderly in the community varied significantly in different stages of sarcopenia and genders, which correlated with sarcopenia.

Influences of muscle mass loss and exercise habits and personality traits on lower limb motor function among university students

Secondary sarcopenia, a risk factor even for young people, has attracted attention because of the deterioration of physical activity and nutritional status due to lifestyle change among university students. However, studies on the factors affecting motor function and their involvement are lacking. This cross-sectional study aimed to examine the influences of muscle mass loss and exercise and sleep habits on lower limb motor function, as well as the involvement of personality traits, in 101 university students. Approximately 6% of the participants had low skeletal muscle mass index, similar to previous reports, and that only exercise habits in high school were responsible for muscle mass loss (direct effect =  - 0.493; p < 0.05), wherease low skeletal muscle mass (direct effect =  - 0.539; p < 0.01) and current exercise habits (direct effect = 0.410; p < 0.01) were responsible for lower limb motor function. Additionaly, only the personality trait of high intellectual curiosity was involved in the establishment of exercise habits in high school, but no other personality traits showed a significant effect. In the prevention of secondary sarcopenia, encouraging sustained exercise habits while considering the influence of different personality traits is expected to prevent the decline in muscle mass and motor function.

A meta-analysis on the impact of resistance training on phase angle in middle-aged and older individuals

PURPOSE

To determine the impact of resistance training (RT) on phase angle (PhA) in middle-aged and older individuals via meta-analysis, explore effects in subgroups, and identify optimal RT protocol.

MATERIALS AND METHODS

We searched five databases using predefined criteria, assessed literature quality per Cochrane 5.1 Handbook, and used Revman 5.3 for effect size aggregation, bias assessment, sensitivity analysis, and subgroup analysis.

RESULTS

RT improved PhA in middle-aged and older individuals (d = 0.34, 95 % CI: 0.27-0.40, P < 0.05). Effective subgroups included Suspension (d = 0.62, 95 % CI: 0.33-0.90, P < 0.05), free-weights and machine (d = 0.36, 95 % CI: 0.28-0.45, P < 0.05), equipment training (d = 0.24, 95 % CI: 0.13-0.36, P < 0.05), and moderate-intensity RT (d = 0.34, 95 % CI: 0.27-0.42, P < 0.05). RT was conducted 2-3 times/week (d = 0.20, 95 % CI: 0.01-0.38, P < 0.05) or (d = 0.38, 95 % CI: 0.30-0.47, P < 0.05). PhA improved after 8 weeks (d = 0.37, 95 % CI: 0.23-0.51, P < 0.05), 12 weeks (d = 0.35, 95 % CI: 0.26-0.44, P < 0.05), and ≥ 24 weeks (d = 0.26, 95 % CI: 0.11-0.41, P < 0.05) of RT in aged and older individuals. Low- and high-intensity RT, elastic band training, and weekly exercises did not significantly improve PhA.

CONCLUSIONS

RT enhances PhA in middle-aged and older adults. For optimal results, we recommend 2-3 weekly sessions of free weights and machine training lasting at least 8 weeks.

Improvement of muscle quality assessed using the phase angle is influenced by recovery of knee extension strength in patients with hip fractures

BACKGROUND AND AIMS

Studies reported that knee extension strength on the operated side in patients with hip fractures was not recovered to the level on the non-operated side 6 months after surgery or later. In a cross-sectional study, we revealed that a reduction in isometric knee extension muscle strength on the operated side in patients with hip fractures approximately 6 months after surgery was associated with not only a reduction in skeletal muscle mass but also a reduction in muscle quality, characterized by a reduction in the phase angle (PhA). Furthermore, the mechanisms of knee extension strength improvement can be clarified in more detail using the minimal significant change as the index of recovery. However, no longitudinal studies have examined the factors for knee extension strength improvement based on the minimal significant change in patients with hip fractures 6 months after surgery. This study aimed to longitudinally examine the factors influencing the recovery of knee extension strength based on the minimal significant change in patients with hip fractures between 2 weeks and approximately 6 months after surgery.

METHODS

In this study, the outcomes used were basic and medical information, PhA, skeletal muscle index (SMI), pain, one-leg standing time, movement control during one-leg standing, and walking speed. For PhA, SMI, pain, one-leg standing time, movement control during one-leg standing, and walking speed, the amount of change was calculated by subtracting the data at 2 weeks from the data at 6 months. Group classification was determined by dividing the patients into two groups using a previous study as a reference: recovery group if the knee extension strength value approximately 6 months after surgery minus that 2 weeks after surgery was ≥3.3 kgf and non-recovery group if the value was <3.3 kgf. Logistic regression analysis was performed to explore the association between the recovery and non-recovery groups.

RESULTS

The recovery group contained 55 patients, while the non-recovery group comprised 35 patients. The only significant factor associated with knee extension muscle strength in the recovery group was the amount of change in PhA. The odds ratio for the amount of change in PhA was 2.26. The discrimination rate of the model was 62.5%.

CONCLUSIONS

Our results suggest that recovery of knee extension strength in patients with hip fractures after surgery was mainly because of improvements in muscle quality, not improvements in muscle mass or pain.

Utilization of bioelectrical impedance vector analysis (BIVA) in children and adolescents without diagnosed diseases: a systematic review

Introduction. Bioelectrical impedance vector analysis (BIVA) emerges as a technique that utilizes raw parameters of bioelectrical impedance analysis and assumes the use of a reference population for information analysis.Objective. To summarize the reference values, main studies objectives, approaches, pre-test recommendations and technical characteristics of the devices employed in studies utilizing BIVA among children and adolescents without diagnosed diseases.Methods. A systematic search was conducted in nine electronic databases (CINAHL, LILACS, PubMed, SciELO, Scopus, SPORTDiscus, Science Direct, MEDLINE, and Web of Science). Studies with different designs which allowed extracting information regarding reference values of BIVA in children and adolescents without diagnosed diseases, aged 19 years or younger, were included. The systematic review followed PRISMA procedures and was registered in PROSPERO (registration: CRD42023391069).Results. After applying the eligibility criteria, 36 studies were included. Twenty studies (55.6%) analyzed body composition using BIVA, thirteen studies (36.1%) aimed to establish reference values for BIVA, and three studies (8.3%) investigated the association of physical performance with BIVA. There was heterogeneity regarding the reference populations employed by the studies. Fifteen studies used their own sample as a reference (41.6%), four studies used the adult population as a reference (11.1%), and five studies used reference values from athletes (13.9%).Conclusion. Nutricional status and body composition were the main studies objectives. References values were not always adequate or specific for the sample and population. Furthermore, there was no pattern of pre-test recommendations among the studies.

Phase angle - A screening tool for malnutrition, sarcopenia, and complications in gastric cancer

BACKGROUND

Patients with gastric cancer (GC) are more likely to experience malnutrition and muscle wasting. This study aims to investigate the potential of phase angle (PhA) as a screening tool for identifying malnutrition and sarcopenia in GC patients, as well as its association with short-term outcomes after radical gastrectomy.

METHODS

This cross-sectional study enrolled patients diagnosed with GC at The Affiliated People's Hospital of Jiangsu University from October 2021 to September 2022. PhA was measured using bioelectrical impedance analysis. Computed tomography scan images were analyzed for body composition at the level of the third lumbar vertebra. Malnutrition was diagnosed using Global Leadership Initiative on Malnutrition (GLIM) criteria. Sarcopenia diagnosis was based on the Asian Working Group for Sarcopenia (AWGS) 2019 criteria.

RESULTS

A total of 248 patients with GC were analyzed, including 188 patients who underwent radical gastrectomy. Of these, 71.4 % (n = 177) were male and 28.6 % (n = 71) were female and the median overall age was 68 years (IQR: 61-72 years). According to GLIM criteria, 49.2 % (n = 122) of patients were malnourished and 19.8 % (n = 49) had sarcopenia based on AWGS criteria. A one-degree decrease in PhA was significantly associated with GLIM malnutrition (Odds Ratio [OR] = 8.108, 95 % CI:3.181-20.665) and sarcopenia (OR = 2.903, 95 % CI:1.170-7.206). PhA exhibited fair to good diagnostic accuracy in identifying GLIM malnutrition (male: AUC = 0.797; female: AUC = 0.816) and sarcopenia (male: AUC = 0.814; female: AUC = 0.710). Low PhA (OR = 3.632, 95 % CI: 1.686-7.824) and operation time (OR = 2.434, 95 % CI:1.120-5.293) were independently associated with the risk of postoperative complications.

CONCLUSIONS

PhA can serve as a reliable screening tool for identifying patients at risk of malnutrition, sarcopenia, and postoperative complications in GC.

EXERT-BC: Prospective Study of an Exercise Regimen After Treatment for Breast Cancer

Purpose EXERT-BC is a dose-escalated resistance training regimen created to improve body composition, strength, and balance in women treated for breast cancer (BC). Herein, we report the interim analysis. Women treated for BC underwent this 3-month exercise regimen in an exercise oncology facility with continual monitoring of load and strength. Twenty women completed the IRB-approved protocol, with a mean age of 57 years (range 41-74). Concurrent therapies included anti-estrogen therapy (73%), chemotherapy (14%), and radiotherapy (23%). 27% of women endorsed prior exercise. Subjects missed an average of 1.75 classes (range 0-7), with all meeting adherence over 75%. No injuries or adverse events were reported aside from muscle soreness and 2 days of knee pain. Significant differences in body composition at completion included reduced body fat (38.2% vs. 36.7%, p=0.003), and increased muscle mass (33.1% vs. 37.1%, p<0.001), functional mobility screening (9.82 vs. 11.73, p=0.018), and Y-balance (left: 72.4 vs. 85.3, p=0.001; right: 70.3 vs. 85.2. p<0.001). Significant increases in load were demonstrated: split squat (p<0.001), trap bar deadlift (p=0.035), inclined dumbbell press (p<0.001), and bird dog rows (p<0.001). Dose-escalated resistance training in women with BC is safe and feasible, endorsing significant improvements across body composition, balance, and strength.

Limb-specific isometric and isokinetic strength in adults: The potential role of regional bioelectrical impedance analysis-derived phase angle

BACKGROUND & AIMS

It is not yet known whether regional bioelectrical impedance (BIA) phase angle (PhA) may be informative of different types of strength performed by the lower and upper limbs, independently of lean soft tissue mass (LSTM). Using a sample of healthy adults, we aimed to examine the association and relevance of regional PhA relative to isometric and isokinetic strength of each limb.

METHODS

A total of 57 participants (32.7 ± 12.9 years; 24.7 ± 3.5 kg/m2) were included in the present investigation. Regional raw BIA variables were determined using a phase-sensitive BIA device. Dual-energy X-ray absorptiometry was used to evaluate LSTM. Absolute isometric and isokinetic (i.e., 60°/s and 180°/s) strength of each limb (extension and flexion) was assessed using an isokinetic dynamometer and used to calculate relative strength.

RESULTS

In absolute strength, only dominant leg PhA was associated with isometric extension strength (β = 0.283) and isokinetic 180°/s flexion strength (β = 0.354), regardless of LSTM (p < 0.05). In relative strength, a significant association of regional PhA was found for dominant arm flexion isometric strength (β = 0.336), and non-dominant arm and dominant leg extension isometric strength (β = 0.377, β = 0.565, respectively; p < 0.05), independently of LSTM. Similarly, for isokinetic 180°/s strength, regional PhA significantly explained the variance in the relative strength of both arms and dominant leg (β = 0.350 to 0.506), regardless of LSTM (p < 0.05). Relative isokinetic 60°/s strength was not consistently associated with regional PhA (p ≥ 0.05).

CONCLUSIONS

Regional PhA significantly explained relative (isometric and 180°/s isokinetic strength of both arms and dominant leg), but not absolute muscle strength, independently of regional LSTM. Thus, after accounting for body size, regional PhA seems to have its own characteristics that explain relative strength independently of LSTM.

Is muscle localized phase angle an indicator of muscle power and strength in young women?

Objective. This study aimed to investigate the capacity of the bioelectrical muscle localized phase angle (ML-PhA) as an indicator of muscle power and strength compared to whole body PhA (WB-PhA).Approach. This study assessed 30 young women (22.1 ± 3.2 years) for muscle power and strength using the Wingate test and isokinetic dynamometer, respectively. Bioimpedance analysis at 50 kHz was employed to assess WB-PhA and ML-PhA. Lean soft tissue (LST) and fat mass (FM) were quantified using dual x-ray absorptiometry. Performance values were stratified into tertiles for comparisons. Regression and mediation analysis were used to test WB-PhA and ML-PhA as performance predictors.Main results. Women in the second tertile of maximum muscle power demonstrated higher ML-PhA values than those in first tertile (13.6° ± 1.5° versus 11.5° ± 1.5°,p= 0.031). WB-PhA was a predictor of maximum muscle power even after adjusting for LST and FM (β= 0.40,p= 0.039). ML-PhA alone predicted average muscle power (β= 0.47,p= 0.008). FM percentage was negatively related to ML-PhA and average muscle power, and it mediated their relationship (b= 0.14; bias-corrected and accelerated 95% confidence interval: 0.007-0.269).Significance. PhA values among tertiles demonstrated no differences and no correlation for strength variables. The results revealed that both WB and ML-PhA may be markers of muscle power in active young women.

Phase angle as a key marker of muscular and bone quality in community-dwelling independent older adults: A cross-sectional exploratory pilot study

The aim of the present cross-sectional exploratory pilot study was to analyze the ability of the Phase Angle (PhA) to predict physical function, muscle strength and bone indicators, upon adjusting for potential confounders [age, sex, lean mass, and body mass index (BMI)]. This study included 56 physically independent older adults (age, 68.29 ± 3.01 years; BMI, 28.09 ± 4.37 kg/m2). A multi-frequency segmental bioelectrical impedance analysis was used to measure PhA at 50 KHz. Additionally, physical function was assessed through four functional capacity tests [30-sec chair-stand; seated medicine ball throw (SMBT); timed up & go; and 6-min walking test (6 MWT)], muscle strength through the handgrip test (dominant side) and maximal isokinetic strength of the dominant knee flexor and extensor. Moreover, bone indicators and body composition were assessed through the dual energy X-ray absorptiometry. PhA was significantly associated with SMBT (r = 0.375, effect size (ES) = moderate); 6 MWT (r = 0.396, ES = moderate); 30-sec chair-stand (rho = 0.314, ES = moderate); knee extension (rho = 0.566, ES = large) and flexion (r = 0.459, ES = moderate); handgrip (rho = 0.432, ES = moderate); whole-body bone mineral content (BMC) (r = 0.316, ES = moderate); femoral neck BMC (r = 0.469, ES = moderate); and femoral neck bone mineral density (BMD) (rho = 0.433, ES = moderate). Additionally, the results of multiple regression analysis demonstrated that PhA is significantly associated with SMBT (p < 0.001; R2 = 0.629), 6 MWT (p = 0.004; R2 = 0.214), knee extension (p < 0.001; R2 = 0.697), knee flexion (p < 0.001; R2 = 0.355), handgrip test (p < 0.001; R2 = 0.774), whole-body BMC (p < 0.001; R2 = 0.524), femoral neck BMC (p = 0.001; R2 = 0.249), and femoral neck BMD (p = 0.020; R2 = 0.153). The results of the preliminary analysis suggested that PhA is linked to muscle strength and some factors related to physical function and bone quality in community-dwelling older adults.

Bioelectrical impedance phase angle is associated with physical performance before but not after simulated multi-stressor military operations

Physical performance decrements observed during multi-stressor military operations may be attributed, in part, to cellular membrane dysfunction, which is quantifiable using phase angle (PhA) derived from bioelectrical impedance analysis (BIA). Positive relationships between PhA and performance have been previously reported in cross-sectional studies and following longitudinal exercise training programs, but whether changes in PhA are indicative of acute decrements in performance during military operations is unknown. Data from the Optimizing Performance for Soldiers II study, a clinical trial examining the effects of exogenous testosterone administration on body composition and performance during military stress, was used to evaluate changes in PhA and their associations with physical performance. Recreationally active, healthy males (n = 34; 26.6 ± 4.3 years; 77.9 ± 12.4 kg) were randomized to receive testosterone undecanoate or placebo before a 20-day simulated military operation, which was followed by a 23-day recovery period. PhA of the whole-body (Whole) and legs (Legs) and physical performance were measured before (PRE) and after (POST) the simulated military operation as well as in recovery (REC). Independent of treatment, PhAWhole and PhALegs decreased from PRE to POST (p < 0.001), and PhALegs , but not PhAWhole , remained lower at REC than PRE. PhAWhole at PRE and REC were associated with vertical jump height and Wingate peak power (p < 0.001-0.050), and PhAWhole at PRE was also associated with 3-RM deadlift mass (p = 0.006). However, PhA at POST and changes in PhA from PRE to POST were not correlated with any performance measure (p > 0.05). Additionally, PhA was not associated with aerobic performance at any timepoint. In conclusion, reduced PhA from PRE to POST provides indirect evidence of cellular membrane disruption. Associations between PhA and strength and power were only evident at PRE and REC, suggesting PhA may be a useful indicator of strength and power, but not aerobic capacity, in non-stressed conditions, and not a reliable indicator of physical performance during severe physiological stress.