[Changes in motor unit activity in the biceps brachii muscle under different intensities of isometric loading]. / A motoros egységek aktivitásának változása a biceps brachii izomban különbözo intenzitású izometriás terhelések hatására.

INTRODUCTION: In patients with cancer, loss of muscle mass is observed in many cases and tumour types. This can lead to a drastic deterioration in the patient's quality of life, with the inability to support themselves. Nowadays, in addition to primary treatment of the tumour, physical training of patients has become a priority in order to maintain their quality of life. One key to this is resistance training to prevent sudden muscle loss, which the patient can do alongside primary treatment, and isometric training may be one option. OBJECTIVE: Our aim was to measure the activation frequency characteristics of the biceps brachii muscle in our subjects during a fatigue protocol while creating a constant controlled isometric tension in the muscle. METHOD: 19 healthy university students participated in our study. After determining the dominant side, the subjects' single repetition maximum was assessed using the GymAware RS tool and then 65% and 85% of this was calculated. We placed electrodes on the biceps brachii muscle and had them hold the weight at 65% and 85% until full fatigue. Immediately afterwards, subjects performed an isometric maximal contraction (Imax). The measured electromyography recordings were divided into 3 equal parts, then the first, middle and last 3 s (W1, W2, W3) were analyzed. RESULTS: Our results show that, consistent with fatigue, at both 1RM 65% and 1RM 85% load, the activity of the low-frequency motor units increases, while the activation of the high-frequency motor units decreases. DISCUSSION: The present study is consistent with our previous study. CONCLUSION: Our test protocol is not suitable for prolonged activation of high-frequency motor units because the activity of high-frequency motor units decreases over time. Orv Hetil. 2023; 164(10): 376-382.

Significantly Delayed Medium-Latency Response of the Stretch Reflex in Delayed-Onset Muscle Soreness of the Quadriceps Femoris Muscles Is Indicative of Sensory Neuronal Microdamage.

Unaccustomed or strenuous eccentric exercise is known to cause delayed-onset muscle soreness. A recent hypothesis postulated that mechano-energetic microinjury of the primary afferent sensory neuron terminals in the muscle spindles, namely a transient Piezo2 channelopathy, could be the critical cause of delayed-onset muscle soreness in the form of a bi-phasic non-contact injury mechanism. This theory includes that this microlesion could delay the medium-latency response of the stretch reflex. Our aim with this study was to investigate this hypothesis. According to our knowledge, no study has examined the effect of delayed-onset muscle soreness on the medium-latency response of the stretch reflex. Our findings demonstrated that a significant delay in the medium-latency stretch reflex could be observed right after a multi-stage fitness test in the quadriceps femoris muscles of Hungarian professional handball players who consequently experienced delayed-onset muscle soreness. The long-latency stretch reflex and most likely short-latency stretch reflex were unaffected by delayed-onset muscle soreness in our study, which is in line with earlier findings. We translate these findings as indicative of proprioceptive Type Ia terminal microdamage in the muscle spindle in line with the aforementioned new acute non-contact compression axonopathy theory of delayed-onset muscles soreness.

Comparison of Shear Wave Elastography and Dynamometer Test in Muscle Tissue Characterization for Potential Medical and Sport Application.

Skeletal muscle status and its dynamic follow up are of particular importance in the management of several diseases where weight and muscle mass loss and, consequently, immobilization occurs, as in cancer and its treatment, as well as in neurodegenerative disorders. But immobilization is not the direct result of body and muscle mass loss, but rather the loss of the maximal tension capabilities of the skeletal muscle. Therefore, the development of a non-invasive and real-time method which can measure muscle tension capabilities in immobile patients is highly anticipated. Our aim was to introduce and evaluate a special ultrasound measurement technique to estimate a maximal muscle tension characteristic which can be used in medicine and also in sports diagnostics. Therefore, we determined the relationship between the results of shear wave elastography measurements and the dynamometric data of individuals. The measurements were concluded on the m. vastus lateralis. Twelve healthy elite athletes took part in our preliminary proof of principle study-five endurance (S) and seven strength (F) athletes showing unambiguously different muscle composition features, nine healthy subjects (H) without prior sports background, and four cancer patients in treatment for a stage 3 brain tumor (T). Results showed a high correlation between the maximal dynamometric isometric torque (Mmax) and mean elasticity value (E) for the non-athletes [(H + T), (r = 0.795)] and for the athletes [(S + F), (r = 0.79)]. For the athletes (S + F), the rate of tension development at contraction (RTDk) and E correlation was also determined (r = 0.84, p < 0.05). Our measurements showed significantly greater E values for the strength athletes with fast muscle fiber dominance than endurance athletes with slow muscle fiber dominance (p < 0.05). Our findings suggest that shear wave ultrasound elastography is a promising method for estimating maximal muscle tension and, also, the human skeletal muscle fiber ratio. These results warrant further investigations with a larger number of individuals, both in medicine and in sports science.

Adaptation of Fatigue Affected Changes in Muscle EMG Frequency Characteristics for the Determination of Training Load in Physical Therapy for Cancer Patients.

Cancer patients often experience loss in body weight and also a decrease in muscle mass, which results in the reduction of physical activity and mobilization of the patient. To decelerate the loss of muscle mass, as part of the cancer treatment patients frequently undergo physical therapy and considering the physical capabilities of the patients, with moderate loads. Moreover, frequent studies also observed for cancer patients, together with the decrease in muscle mass a shift into fast-twitch muscle fibers from slow-twitch fibers. The aim of our study therefore was to determine how motor fibers behave under moderate isometric load executed until total exhaustion. 11 university students (G1), and 14 elite athletes (G2) participated in the study. 65% of the maximal voluntary contraction (MVC) was determined for the biceps brachii muscle, and with this load holding a weight, participants had to sustain a 90 deg. isometric elbow flexion in a standing posture until complete fatigue occurred. EMG activity for the biceps brachii muscle was measured and frequency analysis was performed. 3 windows were determined in the fatiguing protocol: the first (W1), middle (W2), and last (W3) 5 s, and also frequency analysis for MVC was performed (MAX) between 0 and 260 Hz with 20 Hz wide frequency bands. The results indicate, that as the protocol progressed in time and the effect of fatigue increased (from W1 to W3) the activity of low frequency muscle fibers significantly increased (0-40 Hz) while activity of high frequency muscle fibers (60-260 Hz) significantly decreased for G1 and G2 groups identically. We can conclude, that training applied with constant moderate tension as fatigue increases will result in the increased activation of the lower frequency slow-twitch muscle fibers, but the increase of fatigue in the lower frequency fibers will not result in the increase in the activation level of the higher frequency fast-twitch fibers. Consequently, because as slow-twitch fibers are being used at moderate loads and even when fatigue occurs in these fibers the fast-twitch fibers will not work, higher muscle loads are needed if the aim is to activate fast-twitch fibers. Considering the shift into fast-twitch muscle fibers from slow-twitch fibers for cancer patients, in some cases if the patient's age and physical status allows during the physical treatment, higher loads and consequently higher levels of activation might be beneficial for the retardment of loss concerning the fast-twitch fiber mass.