Muscles, Volume 3, Issue 4 (December 2024) – 8 articles

Background: Surface mechanomyographic (sMMG) signals have been used to examine sex-specific differences in the mechanical behavior of muscle during fatiguing exercise. However, studies often utilize simple amplitude- and frequency-based analyses, which only reveal the static components of the sMMG signal. Methods: Thus, a wavelet-based analysis was used to examine changes in the spectral intensity of the non-dominant limb’s vastus lateralis during a fatiguing, maximal, unilateral isometric leg extension in recreationally active men (n = 11) and women (n = 10). Relative changes in spectral intensities and instantaneous mean frequency (IMF) were examined using linear mixed-effect models. Time-to-task failure was compared using an independent sample t-test. Results: The neuromuscular responses demonstrated parallel decreases in IMF (p < 0.001). Further, there were parallel, nonlinear, decreases in spectral intensity across wavelets (p < 0.001) and there were no sex differences in time-to-task failure (p = 0.15). Conclusions: These data showed no sex-specific differences in exercise fatigability or muscle mechanics during fatiguing exercise of the leg extensors. However, when collapsed across sex, wavelet-specific changes in spectral intensity over time reveal novel insights into the interplay between low- and high-frequency components during fatigue. Full article

Maximal eccentric (MES) and isometric (MIS) muscle strength may enhance vertical jump performance by facilitating preloading and reducing energy loss during the eccentric (ECC) phase of the stretch-shortening cycle (SSC). However, the contributions of ECC and isometric (ISO) strength to the countermovement (CMJ) and depth jump (DJ) remain unclear due to variability in assessment methods (e.g., dynamometry, isometric mid-thigh pull) and the limited range of metrics examined in prior research. The aim of this study was to assess correlations between multi-joint lower extremity MES and MIS, obtained using a seated multi-joint isokinetic dynamometer, and 13 vertical ground reaction force (GRF) measures derived from the performance of three maximal effort DJs and CMJs. Twenty-five healthy young adults participated in this study (age = 21.9 ± 2.9 years). Pearson r correlation coefficients were used to assess the statistical significance (α = 0.05) of the relationships between absolute (N) and body mass normalized (BN) maximal strength measures and vertical jumping metrics. Moderate-to-strong positive correlations were identified between MES and MIS with broad performance metrics in CMJ and DJ, including reactive strength index (r = 0.45–0.53, p < 0.05), modified reactive strength index (r = 0.41–0.62, p < 0.05), and jump height (r = 0.59–0.75, p < 0.05). Moderate-to-strong positive correlations were also observed between MES and MIS with CON work (r = 0.58–0.71, p < 0.05) and CON peak power (r = 0.44–0.71, p < 0.05) for both the CMJ and DJ. In contrast, moderate-to-strong negative correlations were observed between MES and MIS with ECC work (r = 0.42–0.62, p < 0.005) and ECC peak power (r = 0.45–0.60, p < 0.05). These findings suggest that enhanced neuromuscular efficiency and joint stiffness in stronger musculature reduce energy absorption during the eccentric phase, minimizing mechanical deformation and preserving elastic energy for concentric propulsion. Combined, MES and MIS optimize force application, energy utilization, and control, which are crucial for maximizing jump height. These findings underscore the role of MES and MIS in influencing jumping performance across both the ECC and CON phases of the SSC. This insight is valuable for practitioners designing training programs aimed at improving vertical jumping ability. Full article

People affected by mitochondrial myopathies (MITOs) are thought to have impaired skeletal muscle oxygenation. The aims of this study were to measure skeletal muscle mitochondrial capacity in MITO participants and able-bodied (AB) participants and evaluate the influence of muscle-specific endurance training in one MITO participant. Participants (n = 7) with mitochondrial disease and controls (n = 9) were tested (ages 18–54 years). Mitochondrial capacity (mVO₂max) was measured using the rate constant of recovery of oxygen consumption (mVO₂) after exercise in the forearm flexor muscles with near-infrared spectroscopy (NIRS). One MITO participant was tested before and after performing 18 forearm exercise sessions in 30 days. There were no differences between MITO and AB participants in mVO₂max (MITO: 1.4 ± 0.1 min⁻¹; AB: 1.5 ± 0.3 min⁻¹; p = 0.29), resting mVO₂ (MITO: −0.4 ± 0.2%/min; AB: −0.3 ± 0.1%/min; p = 0.23), or initial post exercise oxygen consumption rates (MITO: 4.3 ± 1.2%/min; AB: 4.4 ± 1.4%/min; p = 0.9). Exercise oxygen desaturation was greater in MITO (39.8 ± 9.7% range) than in AB (28 ± 8.8% range) participants, p = 0.02. The MITO participant who trained increased her mitochondrial capacity (58%) and muscle-specific endurance (24%) and had reduced symptoms of muscle fatigue. We found no evidence supporting in vivo impairment of forearm muscle mVO₂max in genetically confirmed MITO participants. This is consistent with studies that report increased mitochondrial content, which offsets the decrease in mitochondrial function. Positive muscle adaptations to endurance training appear to be possible in people with MITOs. Characterization of study populations will be important when interpreting the relationship between in vivo mitochondrial capacity and mitochondrial disease. Full article

Background: The presence of sensorimotor control deficits in adolescent idiopathic scoliosis compared to typically developed adolescents is supported by the literature but lacks reliability studies for assessment in this population. This study aimed to assess the reliability of eight sensorimotor control tests, in terms of static and dynamic balance, joint position sense (JPS) tests of the extremities and the spine, and a functional upper extremity proprioceptive test in adolescent idiopathic scoliosis subjects. Methods: Sixty adolescent idiopathic scoliosis subjects were divided into four groups. Each group underwent two tests by the same examiner, repeated at 15 min intervals. Reliability was measured using the intraclass correlation coefficient (ICC), standard error of measurement (SEM), and smallest detectable difference (SDD). Results: The results showed high reliability for the upper extremity functional proprioception test, for the dynamic and static balance test, and for the spinal lateral flexion joint position sense test in both directions. On the other hand, the shoulder external rotation, knee extension, elbow flexion, and spinal flexion joint position sense tests demonstrated poor reliability in adolescent idiopathic scoliosis subjects. Conclusions: Therapists are recommended to use the functional upper extremity proprioception test, the Fukuda test, the static balance test using a force footplate, and the spinal lateral flexion joint position sense test for assessing treatment progress in this population. Full article

Turkesterone is a naturally occurring plant steroid touted for its medicinal, pharmacological, and biological properties with no reported adverse side effects compared with traditional anabolic androgenic steroids (AAS). However, this ostensible enhancement to increase muscle protein synthesis and facilitate augmented thermogenesis remains undescribed despite uninformed and potentially haphazard consumption. To investigate whether turkesterone enhances insulin-like growth factor-1 (IGF-1) and resting metabolic rate (RMR), eleven apparently healthy males (23.3 ± 2.2) volunteered to participate in the present study with samples collected pre-, 3H post-, and 24H post-ingestion. Subsequent analyses failed to reveal any significant main condition, time, or interaction main effects for serum IGF-1, RMR, lipid, and carbohydrate metabolism (p > 0.05). However, non-significant serum IGF-1 concentrations increased with both turkesterone conditions and remained elevated when compared with placebo. Similarly, RMR remained elevated above baseline across the 3 h assessed. Although these data fail to fully support turkesterone as a potent anabolic supplement, nevertheless, our findings are foundational to persistently tease apart this supplement’s purported ergogenic effects and underscore its favorable hemodynamic and gastrointestinal tolerability profile. Future investigations should, therein, aim to assess turkesterone-mediated IGF-1 increases on long-term whole-muscle growth across several training sessions to further substantiate its efficacy on anabolism. Full article

Introduction: The physiological response of the tendon structure has been the subject of several studies using clinical thermography, although the lack of normal values limits clinical practice despite being, according to several authors, an optimal diagnostic tool for the study and therapeutic monitoring of soft tissues. To this end, the aim of this systematic review was to explore all the scientific information on thermography and reference values in the patellar tendon. Method: A search was carried out in different health science databases using the MeSH terms “Health”, “Patellar Ligament”, and “Thermography” with their synonyms in free terms to collect the studies to be included in the systematic review. This review was conducted according with PRISMA guidelines and includes all of the literature up to 19 December 2023. All studies that were in accordance with the PICOS strategy in title and abstract were included in this review, while studies that performed the baseline thermographic test in an altered physiological state were excluded after reading the full text. The TISEM scale was used to assess the quality of the studies; the risk of bias was assessed with the QUADAS-2 scale. Result: A total of 6 articles was selected (n = 148); these were analyzed for quality and found to be highly heterogenous; the risk of bias was low in most domains of the QUADAS-2 scale. Discussion and Conclusion: There are several variabilities that can induce changes in the thermoregulation process distorting the thermograms. Looking deeper into the evidence behind each item, we can deduce the need to follow the TISEM protocol as closely as possible for an accurate response. The heterogeneity in the way the results were provided and the low quality in some of the studies did not allow for a reference of thermographic values to be obtained. Full article

Construction work is physically demanding. The tasks involved in this professional occupation physically exhaust workers and put them at high risk of injury. This work aimed to analyze muscle fatigue in civil construction workers with and without a history of physical activity. For this purpose, the muscle activity of the biceps femoris, trapezius transversalis, and erector spinae longissimus muscles was evaluated using surface electromyography. Eleven male civil construction workers aged 26 to 52 years (38.00 ± 9.60), seven of whom were untrained (N = 7) and four of whom were trained (N = 4), participated in this study. Each subject completed two assessments at two different times. A questionnaire was completed for the first assessment, and each subject’s maximum repetition for the deadlift exercise was assessed. In the second assessment, the subjects were assessed while performing the deadlift in four different situations: 50%RM at rest, 70%RM at rest, 70%RM at fatigue, and 50%RM at fatigue. The trained construction workers had higher levels of muscle activity, and there were no significant differences in muscle activation between the fatigued and non-fatigued sets. There appears to be a strong influence of physical exercise on muscle activity and fatigue in civil construction workers. Full article

Medial gastrocnemius silent contractures (MGSCs) are prevalent, notably impacting functional status and increasing the risk of foot and ankle disorders, especially among aging populations. Although traditionally managed by podiatrists and physiotherapists, the role of rehabilitation nursing in addressing MGSCs is gaining recognition. This paper elucidates the contributions of rehabilitation nursing to the functional rehabilitation of MGSC patients and underscores its vital role within the multidisciplinary team. Initially, the paper defines the clinical and physiological characteristics of MGSCs and their implications in foot and ankle disorders. It then meticulously explores rehabilitation nursing interventions—including personalized stretching regimens, vibration therapy, balance exercises, and judicious footwear selection—emphasizing their efficacy in enhancing muscle flexibility, joint mobility, and postural stability. The emphasis is on patient-centered approaches and education to foster treatment adherence and positive rehabilitation outcomes. The significance of interdisciplinary collaboration is highlighted, focusing on how rehabilitation nursing optimizes patient care and mitigates complications. The paper advocates for recognizing and integrating rehabilitation nursing in managing MGSC-related disorders, emphasizing its importance in achieving successful functional outcomes. Full article