This chapter addresses the issue of associating the location and nature of the electric field sou... more This chapter addresses the issue of associating the location and nature of the electric field sources below the surface of a conductive medium with the corresponding potential distribution on that surface. Single-point sources (monopoles), pairs of opposite sources (dipoles), and pairs of dipoles (tripoles or quadrupoles) are investigated together with the detection modalities of the surface potential (monopolar, differential, etc.). The electric potentials generated by sources moving under these detection systems are described using a qualitative approach. The general concept of a spatial filter is introduced.
The aim of the study was to non-invasively determine if vastus lateralis (VL) and vastus medialis... more The aim of the study was to non-invasively determine if vastus lateralis (VL) and vastus medialis obliquus (VM) muscles are equally affected by age-related fiber atrophy. Multichannel surface electromyography was used since it allows to estimate muscle fiber conduction velocity (CV), which has been demonstrated to be related to the size of recruited muscle fibers. Twelve active elderly men (age 69 ± 4 years) and 12 active young men (age 23 ± 2 years) performed isometric knee extension at 30%, 50%, and 70% of maximal voluntary contraction. Electromyographic signals were recorded from VL and VM muscles of the dominant limb using arrays with eight electrodes and CVs were estimated for each contraction. CV estimates showed a different behavior in the two muscles: in VL at 50% and 70% of maximum voluntary contraction they were greater in young than in elderly; whereas such a difference was not observed in VM. This finding suggest that in active elderly VM seems to be less affected by the age-related fibers atrophy than VL. Hence, the common choice of studying VL as a muscle representative of the whole quadriceps could generate misleading findings. Indeed, it seemed that the sarcopenic ageing effects might be heterogeneous within quadriceps muscle.
Objectives: Advances in surface electromyography (sEMG) techniques provide a clear indication tha... more Objectives: Advances in surface electromyography (sEMG) techniques provide a clear indication that refinement of electrode location relative to innervation zones (IZ) is required in order to optimise the accuracy, relevance and repeatability of the sEMG signals. The aim of this study was to identify the IZ for the sternocleidomastoid and anterior scalene muscles to provide guidelines for electrode positioning for future clinical and research applications. Methods: Eleven volunteer subjects participated in this study. Myoelectric signals were detected from the sternal and clavicular heads of the sternocleidomastoid and the anterior scalene muscles bilaterally using a linear array of 8 electrodes during isometric cervical flexion contractions. The signals were reviewed and the IZ(s) were identified, marked on the subjects' skin and measurements were obtained relative to selected anatomical landmarks. Results: The position of the IZ lay consistently around the mid-point or in the superior portion of the muscles studied. Conclusions: Results suggest that electrodes should be positioned over the lower portion of the muscle and not the mid-point, which has been commonly used in previous studies. Recommendations for sensor placement on these muscles should assist investigators and clinicians to ensure improved validity in future sEMG applications.
Over the past decade, linear and nonlinear surface electromyography (EMG) variables highlighting ... more Over the past decade, linear and nonlinear surface electromyography (EMG) variables highlighting different components of fatigue have been developed. In this study, we tested fractal dimension (FD) and conduction velocity (CV) rate of changes as descriptors, respectively, of motor unit synchronization and peripheral manifestations of fatigue. Sixteen elderly (69 ± 4 years) and seventeen young (23 ± 2 years) physically active men (almost 3-5 h of physical activity per week) executed one knee extensor contraction at 70% of a maximal voluntary contraction for 30 s. Muscle fiber CV and FD were calculated from the multichannel surface EMG signal recorded from the vastus lateralis and medialis muscles. The main findings were that the two groups showed a similar rate of change of CV, whereas FD rate of change was higher in the young than in the elderly group. The trends were the same for both muscles.
Because rate of force development (RFD) is an emerging outcome measure for the assessment of neur... more Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for eva...
European Journal of Physical and Rehabilitation Medicine, 2021
BACKGROUND Fatigue in Parkinson's Disease (PD) compromises patients' physical activity an... more BACKGROUND Fatigue in Parkinson's Disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. As a consequence, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue. AIM To assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects. DESIGN Observational controlled study. POPULATION Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥ 2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: Mini Mental State Examination ≤ 24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatiguerelated conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched. METHODS All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fibre conduction velocity, increase of average rectified value. RESULTS No statistical differences where observed between groups for sEMG variables and muscular electric behaviour in all contraction conditions (all p> .05). CONCLUSIONS Our results show that parkinsonian muscles does not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility. CLINICAL REHABILITATION IMPACT In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.
Results: Among the 221 initial features, the DT selected only 84 features. The overall recognitio... more Results: Among the 221 initial features, the DT selected only 84 features. The overall recognition performance was equal to 90.5%. Specifically, the correct classification percentages for each activity after post-processing were the following (mean ± standard deviation across the 76 subjects): 99.9% ± 0.9% for A 1 , 99.2% ± 4.2% for A 2 , 87.3% ± 14.1% for A 3 , 87.6% ± 7.4% for A 4 , 95.8% ± 6.7% for A 5 , 82.7% ± 17.5% for A 6 , 80.8% ± 18.8% for A 7. Discussion: The purpose of this study was obtaining a classifier to be implemented on a wearable microprocessor system able to monitor a subject over a daylong period. To this purpose, the choice of a DT is favorable since it may be implemented in firmware as a set of nested "if. .. then" statements. Moreover, it was sufficient using a reduced set of only 84 features instead of the initial set consisting of 221 features, since only part of the initial set was used for constructing the DT. These two facts cause a strong reduction of the computational cost, making it possible to use a microprocessor with a 32-bit architecture without floating processing unit and, consequently, reducing the power requirements of the system. In terms of classification accuracy, the HAR system herein described was able to recognize correctly 90.5% of ADLs. Among the entire group of activities, the lowest value of correct classification was obtained for uphill and downhill walking (83% and 81%), that sometimes were erroneously classified either as level walking or as ascending/descending stairs. This is probably due to the slight slope of the ramp used in our protocol, which ranged between 10% and 15% (wheelchair ramp). In conclusion, we believe that results so far obtained are accurate enough for most applications of interest in clinics and rehabilitation. Battery life of the system is over 20 hours, making it suitable for a daylong analysis session.
Objective: The neuromuscular quickness capacity can be assessed calculating the rate of torque de... more Objective: The neuromuscular quickness capacity can be assessed calculating the rate of torque development (RTD) during ballistic contractions of maximal (RTDmaximal) or submaximal (RTDsubmaximal) amplitudes. In a series of ballistic contractions of submaximal amplitudes, RTD scaling factor (RTD-SF) represents the slope of the linear regression between achieved peak torques and the corresponding RTD. We firstly investigated if the RTD-SF contributes to predict, together with maximal voluntary torques (MVT), the RTDmaximal. Then, we evaluated the agreement between the z-scores of RTDmaximal and RTDsubmaximal. Approach: MVT of quadriceps and hamstrings muscles were obtained in 22 elite young soccer players. RTD-SF was quantified in a series of ballistic contractions of submaximal and maximal amplitudes. RTDsubmaximal was estimated from the regression relationship between the peak torques and the corresponding RTD. Main results: MVT, RTD-SF and y-intercept accounted all together for 76.9 and 61.2% of the variance in RTDmaximal in quadriceps and hamstrings, respectively. Specifically, RTD-SF accounted for 13.7% and 18.7% of the variance in RTDmaximal respectively. Generally, the agreement between the z-scores of RTDmaximal and RTDsubmaximal was poor both in quadriceps and hamstrings. Significance: These results suggest that RTD-SF may have a functional relevance in the relationship between MVT and RTDmaximal and influence the amount of torque that can be achieved in a quick muscle contraction. Moreover, evaluating the RTDsubmaximal does not provide interchangeable results with RTDmaximal. Thus, evaluating the RTD across the whole range of torque could provide additional meaningful information about neuromuscular quickness.
The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks ... more The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or nearmaximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (−12, −12, −21, and −19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.
ABSTRACT Carpal Tunnel syndrome (CTS) is one of the most common compartmental syndromes and nerve... more ABSTRACT Carpal Tunnel syndrome (CTS) is one of the most common compartmental syndromes and nerve conduction studies are widely considered as the standard to diagnose the pathology. The purpose of this pilot study was to investigate whether multichannel surface electromyography can detect muscle alterations in patients diagnosed with severe CTS. Surface EMG signals were recorded at 10, 20, 30, and 80% MVC from the flexor and abductor pollicis brevis muscles of five patients with CTS and five control subjects. Subjects with severe CTS showed different interference patterns, lower signal amplitude, lower neuromuscular efficiency, and lower myoelectric manifestations of fatigue with respect to the control group. At submaximal levels, action potentials recorded from the flexor and abductor pollicis brevis muscles of the CTS group were characterized by lower conduction velocity and lower mean spectral frequency than the healthy group. These findings support, among others, the hypothesis of a selective loss of fast motor units (type II fiber) associated with CTS.
The theoretical approach described in Part I of this book provides the reader with useful informa... more The theoretical approach described in Part I of this book provides the reader with useful information on three important issues: (1) how to record and analyze sEMG signals, (2) what information can be extracted from these signals, and (3) how this information should be interpreted. Until relatively recently, a detailed processing and interpretation of sEMG signals was deemed unnecessary due to the lack of awareness of the influence of electrode location on the quality and quantity of the obtainable information. As is often (if not always) the case, technological evolution provided new tools that increased our capability to understand issues related to volume conduction, the location of innervation zones, motor-unit recruitment strategies, etc. In particular, the innervation zone (IZ) of a fusiform muscle parallel to the skin has now been clearly identified as the worst site to place a pair of recording electrodes. This area (often incorrectly called the neuromuscular junction or motor end plate) is the physical region where the central (-motor neuron terminations) and peripheral (muscle fibers) systems connect through special synapses: the neuromuscular junctions, or end plates. From each of these junctions, action potentials travel in opposite directions, toward the tendon terminations, and generate propagating potentials on the skin. As described in Part I, this issue is not relevant to pinnate muscles, as their fibers are not parallel to the skin. According to a naive earlier approach, electrodes were placed in the middle of the muscle, over its bulk (or belly), since that zone is not only easy to identify by palpation but it also offers the greatest amount of muscle volume, corresponding (presumably!) to the largest EMG signal. This is a good example of an incorrect syllogism. Since the most common electrode montage is differential, it is clear that, if the IZ falls underneath the electrode pair, the resulting signal will be very small and noisy and highly affected by small electrode displacements. Indeed, in this case, signals generated by action potentials traveling toward one tendon are subtracted from similar signals generated by action potentials traveling in the opposite direction, with a resulting output that is small and noisy and often close to zero. Moreover, during dynamic contractions, the relative movement of the muscle with respect to the skin (that is the electrode system) determines a strong alteration of the signal when the IZ shifts under the electrode pair.
ALBERTO RAINOLDI, TOSHIO MORITANI, AND GENNARO BOCCIA Professor of Physiology, Department of Medi... more ALBERTO RAINOLDI, TOSHIO MORITANI, AND GENNARO BOCCIA Professor of Physiology, Department of Medical Sciences, Motor Science Research Center, SUISM University of Turin, Turin, Italy Professor of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto, Japan Motor Science Research Center, SUISM University of Turin, Turin, Italy; and CeRiSM Research Center “Sport, Mountain, and Health,” Rovereto (TN), Italy
This chapter addresses the issue of associating the location and nature of the electric field sou... more This chapter addresses the issue of associating the location and nature of the electric field sources below the surface of a conductive medium with the corresponding potential distribution on that surface. Single-point sources (monopoles), pairs of opposite sources (dipoles), and pairs of dipoles (tripoles or quadrupoles) are investigated together with the detection modalities of the surface potential (monopolar, differential, etc.). The electric potentials generated by sources moving under these detection systems are described using a qualitative approach. The general concept of a spatial filter is introduced.
The aim of the study was to non-invasively determine if vastus lateralis (VL) and vastus medialis... more The aim of the study was to non-invasively determine if vastus lateralis (VL) and vastus medialis obliquus (VM) muscles are equally affected by age-related fiber atrophy. Multichannel surface electromyography was used since it allows to estimate muscle fiber conduction velocity (CV), which has been demonstrated to be related to the size of recruited muscle fibers. Twelve active elderly men (age 69 ± 4 years) and 12 active young men (age 23 ± 2 years) performed isometric knee extension at 30%, 50%, and 70% of maximal voluntary contraction. Electromyographic signals were recorded from VL and VM muscles of the dominant limb using arrays with eight electrodes and CVs were estimated for each contraction. CV estimates showed a different behavior in the two muscles: in VL at 50% and 70% of maximum voluntary contraction they were greater in young than in elderly; whereas such a difference was not observed in VM. This finding suggest that in active elderly VM seems to be less affected by the age-related fibers atrophy than VL. Hence, the common choice of studying VL as a muscle representative of the whole quadriceps could generate misleading findings. Indeed, it seemed that the sarcopenic ageing effects might be heterogeneous within quadriceps muscle.
Objectives: Advances in surface electromyography (sEMG) techniques provide a clear indication tha... more Objectives: Advances in surface electromyography (sEMG) techniques provide a clear indication that refinement of electrode location relative to innervation zones (IZ) is required in order to optimise the accuracy, relevance and repeatability of the sEMG signals. The aim of this study was to identify the IZ for the sternocleidomastoid and anterior scalene muscles to provide guidelines for electrode positioning for future clinical and research applications. Methods: Eleven volunteer subjects participated in this study. Myoelectric signals were detected from the sternal and clavicular heads of the sternocleidomastoid and the anterior scalene muscles bilaterally using a linear array of 8 electrodes during isometric cervical flexion contractions. The signals were reviewed and the IZ(s) were identified, marked on the subjects' skin and measurements were obtained relative to selected anatomical landmarks. Results: The position of the IZ lay consistently around the mid-point or in the superior portion of the muscles studied. Conclusions: Results suggest that electrodes should be positioned over the lower portion of the muscle and not the mid-point, which has been commonly used in previous studies. Recommendations for sensor placement on these muscles should assist investigators and clinicians to ensure improved validity in future sEMG applications.
Over the past decade, linear and nonlinear surface electromyography (EMG) variables highlighting ... more Over the past decade, linear and nonlinear surface electromyography (EMG) variables highlighting different components of fatigue have been developed. In this study, we tested fractal dimension (FD) and conduction velocity (CV) rate of changes as descriptors, respectively, of motor unit synchronization and peripheral manifestations of fatigue. Sixteen elderly (69 ± 4 years) and seventeen young (23 ± 2 years) physically active men (almost 3-5 h of physical activity per week) executed one knee extensor contraction at 70% of a maximal voluntary contraction for 30 s. Muscle fiber CV and FD were calculated from the multichannel surface EMG signal recorded from the vastus lateralis and medialis muscles. The main findings were that the two groups showed a similar rate of change of CV, whereas FD rate of change was higher in the young than in the elderly group. The trends were the same for both muscles.
Because rate of force development (RFD) is an emerging outcome measure for the assessment of neur... more Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the “gold standard” measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for eva...
European Journal of Physical and Rehabilitation Medicine, 2021
BACKGROUND Fatigue in Parkinson's Disease (PD) compromises patients' physical activity an... more BACKGROUND Fatigue in Parkinson's Disease (PD) compromises patients' physical activity and poses questions on how to plan correct rehabilitation training. In addition, the relationship between subjective perceived fatigue and fatigue in motor performance is not yet entirely understood. As a consequence, a conclusive interpretation of muscular mechanisms of fatigue in PD has not yet been achieved. Among the various instrumental evaluations for fatigue, multichannel surface electromyography (sEMG) is a recognized tool that permits the study of myoelectric manifestations of fatigue. AIM To assess if muscles in PD show a different myoelectric fatigue pattern compared to the muscles of healthy age-matched subjects. DESIGN Observational controlled study. POPULATION Idiopathic Parkinson's Disease, Hohen &Yahr II and III stage, Parkinsonian Fatigue Scale average score ≥ 2.95, no therapy modification in the 4 weeks preceding the study; exclusion criteria: Mini Mental State Examination ≤ 24, upper limb disease/symptoms that might interfere with sEMG analysis, presence of other fatiguerelated conditions. Twenty patients were selected according to these criteria. Twenty untrained healthy subjects were matched. METHODS All subjects underwent a muscle fatigue protocol and a sEMG analysis of the right biceps brachii muscle during electrically stimulated and voluntary contractions in order to obtain a myoelectric fatigue muscular pattern. The myoelectric pattern is characterized by the modifications of the following sEMG variables: reduction of mean frequency and muscle fibre conduction velocity, increase of average rectified value. RESULTS No statistical differences where observed between groups for sEMG variables and muscular electric behaviour in all contraction conditions (all p> .05). CONCLUSIONS Our results show that parkinsonian muscles does not differ from the muscles of healthy age-matched subjects in developing peripheral myoelectric fatigue. Nevertheless, the role of fatigue perception at rest and particularly during physical activity must be clearly understood in order to further target the rehabilitative approach for fatigued parkinsonian patients and to reduce hypomobility. CLINICAL REHABILITATION IMPACT In rehabilitative terms, these findings allow us to highlight the possibility of performing sustained training with isometric contractions in PD subjects; therefore, fatigue "per se" does not constitute a barrier for the execution of muscular exercises, likewise intensive.
Results: Among the 221 initial features, the DT selected only 84 features. The overall recognitio... more Results: Among the 221 initial features, the DT selected only 84 features. The overall recognition performance was equal to 90.5%. Specifically, the correct classification percentages for each activity after post-processing were the following (mean ± standard deviation across the 76 subjects): 99.9% ± 0.9% for A 1 , 99.2% ± 4.2% for A 2 , 87.3% ± 14.1% for A 3 , 87.6% ± 7.4% for A 4 , 95.8% ± 6.7% for A 5 , 82.7% ± 17.5% for A 6 , 80.8% ± 18.8% for A 7. Discussion: The purpose of this study was obtaining a classifier to be implemented on a wearable microprocessor system able to monitor a subject over a daylong period. To this purpose, the choice of a DT is favorable since it may be implemented in firmware as a set of nested "if. .. then" statements. Moreover, it was sufficient using a reduced set of only 84 features instead of the initial set consisting of 221 features, since only part of the initial set was used for constructing the DT. These two facts cause a strong reduction of the computational cost, making it possible to use a microprocessor with a 32-bit architecture without floating processing unit and, consequently, reducing the power requirements of the system. In terms of classification accuracy, the HAR system herein described was able to recognize correctly 90.5% of ADLs. Among the entire group of activities, the lowest value of correct classification was obtained for uphill and downhill walking (83% and 81%), that sometimes were erroneously classified either as level walking or as ascending/descending stairs. This is probably due to the slight slope of the ramp used in our protocol, which ranged between 10% and 15% (wheelchair ramp). In conclusion, we believe that results so far obtained are accurate enough for most applications of interest in clinics and rehabilitation. Battery life of the system is over 20 hours, making it suitable for a daylong analysis session.
Objective: The neuromuscular quickness capacity can be assessed calculating the rate of torque de... more Objective: The neuromuscular quickness capacity can be assessed calculating the rate of torque development (RTD) during ballistic contractions of maximal (RTDmaximal) or submaximal (RTDsubmaximal) amplitudes. In a series of ballistic contractions of submaximal amplitudes, RTD scaling factor (RTD-SF) represents the slope of the linear regression between achieved peak torques and the corresponding RTD. We firstly investigated if the RTD-SF contributes to predict, together with maximal voluntary torques (MVT), the RTDmaximal. Then, we evaluated the agreement between the z-scores of RTDmaximal and RTDsubmaximal. Approach: MVT of quadriceps and hamstrings muscles were obtained in 22 elite young soccer players. RTD-SF was quantified in a series of ballistic contractions of submaximal and maximal amplitudes. RTDsubmaximal was estimated from the regression relationship between the peak torques and the corresponding RTD. Main results: MVT, RTD-SF and y-intercept accounted all together for 76.9 and 61.2% of the variance in RTDmaximal in quadriceps and hamstrings, respectively. Specifically, RTD-SF accounted for 13.7% and 18.7% of the variance in RTDmaximal respectively. Generally, the agreement between the z-scores of RTDmaximal and RTDsubmaximal was poor both in quadriceps and hamstrings. Significance: These results suggest that RTD-SF may have a functional relevance in the relationship between MVT and RTDmaximal and influence the amount of torque that can be achieved in a quick muscle contraction. Moreover, evaluating the RTDsubmaximal does not provide interchangeable results with RTDmaximal. Thus, evaluating the RTD across the whole range of torque could provide additional meaningful information about neuromuscular quickness.
The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks ... more The effect of muscle fatigue on rate of force development (RFD) is usually assessed during tasks that require participants to reach as quickly as possible maximal or nearmaximal force. However, endurance sports require athletes to quickly produce force of submaximal, rather than maximal, amplitudes. Thus, this study investigated the effect of muscle fatigue induced by long-distance running on the capacity to quickly produce submaximal levels of force. Twenty-one male amateur runners were evaluated before and shortly after a half-marathon race. Knee extensors force was recorded under maximal voluntary and electrically evoked contractions. Moreover, a series of ballistic contractions at different submaximal amplitudes (from 20 to 100% of maximal voluntary force) was obtained, by asking the participants to reach submaximal forces as fast as possible. The RFD was calculated for each contraction. After the race, maximal voluntary activation, resting doublet twitch, maximal force, and RFD during maximal contraction decreased (−12, −12, −21, and −19%, respectively, all P-values < 0.0001). Nevertheless, the RFD values measured during ballistic contractions up to 60% of maximal force were unaffected (all P-values > 0.4). Long-distance running impaired the capacity to quickly produce force in ballistic contractions of maximal, but not of submaximal, amplitudes. Overall, these findings suggest that central and peripheral fatigue do not affect the quickness to which muscle contracts across a wide range of submaximal forces. This is a relevant finding for running and other daily life activities that rely on the production of rapid submaximal contractions rather than maximal force levels.
ABSTRACT Carpal Tunnel syndrome (CTS) is one of the most common compartmental syndromes and nerve... more ABSTRACT Carpal Tunnel syndrome (CTS) is one of the most common compartmental syndromes and nerve conduction studies are widely considered as the standard to diagnose the pathology. The purpose of this pilot study was to investigate whether multichannel surface electromyography can detect muscle alterations in patients diagnosed with severe CTS. Surface EMG signals were recorded at 10, 20, 30, and 80% MVC from the flexor and abductor pollicis brevis muscles of five patients with CTS and five control subjects. Subjects with severe CTS showed different interference patterns, lower signal amplitude, lower neuromuscular efficiency, and lower myoelectric manifestations of fatigue with respect to the control group. At submaximal levels, action potentials recorded from the flexor and abductor pollicis brevis muscles of the CTS group were characterized by lower conduction velocity and lower mean spectral frequency than the healthy group. These findings support, among others, the hypothesis of a selective loss of fast motor units (type II fiber) associated with CTS.
The theoretical approach described in Part I of this book provides the reader with useful informa... more The theoretical approach described in Part I of this book provides the reader with useful information on three important issues: (1) how to record and analyze sEMG signals, (2) what information can be extracted from these signals, and (3) how this information should be interpreted. Until relatively recently, a detailed processing and interpretation of sEMG signals was deemed unnecessary due to the lack of awareness of the influence of electrode location on the quality and quantity of the obtainable information. As is often (if not always) the case, technological evolution provided new tools that increased our capability to understand issues related to volume conduction, the location of innervation zones, motor-unit recruitment strategies, etc. In particular, the innervation zone (IZ) of a fusiform muscle parallel to the skin has now been clearly identified as the worst site to place a pair of recording electrodes. This area (often incorrectly called the neuromuscular junction or motor end plate) is the physical region where the central (-motor neuron terminations) and peripheral (muscle fibers) systems connect through special synapses: the neuromuscular junctions, or end plates. From each of these junctions, action potentials travel in opposite directions, toward the tendon terminations, and generate propagating potentials on the skin. As described in Part I, this issue is not relevant to pinnate muscles, as their fibers are not parallel to the skin. According to a naive earlier approach, electrodes were placed in the middle of the muscle, over its bulk (or belly), since that zone is not only easy to identify by palpation but it also offers the greatest amount of muscle volume, corresponding (presumably!) to the largest EMG signal. This is a good example of an incorrect syllogism. Since the most common electrode montage is differential, it is clear that, if the IZ falls underneath the electrode pair, the resulting signal will be very small and noisy and highly affected by small electrode displacements. Indeed, in this case, signals generated by action potentials traveling toward one tendon are subtracted from similar signals generated by action potentials traveling in the opposite direction, with a resulting output that is small and noisy and often close to zero. Moreover, during dynamic contractions, the relative movement of the muscle with respect to the skin (that is the electrode system) determines a strong alteration of the signal when the IZ shifts under the electrode pair.
ALBERTO RAINOLDI, TOSHIO MORITANI, AND GENNARO BOCCIA Professor of Physiology, Department of Medi... more ALBERTO RAINOLDI, TOSHIO MORITANI, AND GENNARO BOCCIA Professor of Physiology, Department of Medical Sciences, Motor Science Research Center, SUISM University of Turin, Turin, Italy Professor of Applied Physiology, Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto, Japan Motor Science Research Center, SUISM University of Turin, Turin, Italy; and CeRiSM Research Center “Sport, Mountain, and Health,” Rovereto (TN), Italy
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