Influence of transducer pressure and examiner experience on muscle active shear modulus measured by shear wave elastography

INTRODUCTION

This study examined the effects of ultrasound transducer pressure and examiner experience on the biceps femoris long head and semitendinosus muscle active shear modulus in healthy individuals (n = 28).

METHODS

Active shear modulus was assessed using shear wave elastography at 20% of knee flexor maximal voluntary isometric contraction. Examiners with different experience levels measured the muscles' shear modulus with three pressure levels: mild, moderate, and hard.

RESULTS

A main effect of transducer pressure was found for both biceps femoris long head (p < 0.001; η2p = 0.314) and semitendinosus muscles (p < 0.001; η2p = 0.280), whereas differences were found between mild-moderate (biceps femoris long head: p = 0.013, d = 0.23; semitendinosus: p = 0.024, d = 0.25), and mild-hard pressures (biceps femoris long head: p = 0.001, d = 0.47; semitendinosus: p = 0.002, d = 0.47). Examiners performed similar shear modulus measurements in the biceps femoris long head (p = 0.299; η2p = 0.041) and semitendinosus (p = 0.177; η2p = 0.066), although the experienced examiner showed a higher measurement repeatability (biceps femoris long head: ICC = 0.86-0.95, semitendinosus: ICC = 0.89-0.96; vs. biceps femoris long head: ICC = 0.78-0.87, semitendinosus: ICC = 0.66-0.87).

CONCLUSION

Transducer pressure influences the active shear modulus measurement between mild and moderate or hard pressures. Additionally, examiner experience seems to have no influence on muscle active shear modulus measurement when assessed at the same site (using casts).

IMPLICATIONS FOR PRACTICE

Future studies assessing active muscle shear modulus should use mild transducer pressure and having experienced examiners in order to improve measurement reliability.

Fatigue Evaluation through Machine Learning and a Global Fatigue Descriptor

Research in physiology and sports science has shown that fatigue, a complex psychophysiological phenomenon, has a relevant impact in performance and in the correct functioning of our motricity system, potentially being a cause of damage to the human organism. Fatigue can be seen as a subjective or objective phenomenon. Subjective fatigue corresponds to a mental and cognitive event, while fatigue referred as objective is a physical phenomenon. Despite the fact that subjective fatigue is often undervalued, only a physically and mentally healthy athlete is able to achieve top performance in a discipline. Therefore, we argue that physical training programs should address the preventive assessment of both subjective and objective fatigue mechanisms in order to minimize the risk of injuries. In this context, our paper presents a machine-learning system capable of extracting individual fatigue descriptors (IFDs) from electromyographic (EMG) and heart rate variability (HRV) measurements. Our novel approach, using two types of biosignals so that a global (mental and physical) fatigue assessment is taken into account, reflects the onset of fatigue by implementing a combination of a dimensionless (0-1) global fatigue descriptor (GFD) and a support vector machine (SVM) classifier. The system, based on 9 main combined features, achieves fatigue regime classification performances of 0.82 ± 0.24, ensuring a successful preventive assessment when dangerous fatigue levels are reached. Training data were acquired in a constant work rate test (executed by 14 subjects using a cycloergometry device), where the variable under study (fatigue) gradually increased until the volunteer reached an objective exhaustion state.

Stretching Effects: High-intensity & Moderate-duration vs. Low-intensity & Long-duration

This study examined whether a high-intensity, moderate-duration bout of stretching would produce the same acute effects as a low-intensity, long-duration bout of stretching. 17 volunteers performed 2 knee-flexor stretching protocols: a high-intensity stretch (i. e., 100% of maximum tolerable passive torque) with a moderate duration (243.5 ± 69.5-s); and a low-intensity stretch (50% of tolerable passive torque) with a long duration (900-s). Passive torque at a given sub-maximal angle, peak passive torque, maximal range of motion (ROM), and muscle activity were assessed before and after each stretching protocol (at intervals of 1, 30 and 60 min). The maximal ROM and tolerable passive torque increased for all time points following the high-intensity stretching (p<0.05), but not after the low-intensity protocol (p>0.05). 1 min post-stretching, the passive torque decreased in both protocols, but to a greater extent in the low-intensity protocol. 30 min post-test, torque returned to baseline for the low-intensity protocol and had increased above the baseline for the high-intensity stretches. The following can be concluded: 1) High-intensity stretching increases the maximal ROM and peak passive torque compared to low-intensity stretching; 2) low-intensity, long-duration stretching is the best way to acutely decrease passive torque; and 3) high-intensity, moderate-duration stretching increases passive torque above the baseline 30 min after stretching.

Effects of Walking with Blood Flow Restriction on Excess Post-exercise Oxygen Consumption

This study determined the influence of walking with blood flow restriction (BFR) on the excess post-exercise oxygen consumption (EPOC) of healthy young men. 17 healthy young men (22.1±2.9 years) performed graded treadmill exercise to assess VO_2peak. In a randomized fashion, each participant performed 5 sets of 3-min treadmill exercise at their optimal walking speed with 1-min interval either with or without BFR. Participants were then seated in a chair and remained there for 30 min of recovery. Expired gases were continuously monitored during exercise and recovery. BFR increased the O₂ cost of walking as well as its relative intensity and cumulative O₂ deficit (p<0.05). The EPOC magnitude after walking with BFR was greater than in the non-BFR condition (p<0.05). No differences between conditions were seen for the duration of EPOC. The EPOC magnitude was no longer different between conditions after controlling for the differences in relative intensity and in the cumulative O₂ deficit (p>0.05). These data indicate that walking with BFR increases the magnitude of EPOC. Moreover, they also demonstrate that such increment in EPOC is likely explained by the effects of BFR on walking relative intensity and cumulative O₂ deficit.