SS 153
Myoelectrical and Metabolic Changes in Muscle Fatigue L. Béliveau, Béliveau, J. J. Van Van Hoecke, Hoecke,C. C.Garapon-Bar, Garapon-Bar,E,E.Gaillard, Gaillard,J.I P. P.Herry, Herry,G. G.Atlan, Atlan,P.P.Bouissou Bouissou Laboratoire RMN, Hôpital de Chamonix, Charnonix, Chamoriix, Chamonix, and INSEP, Paris, France
L. Be'liveau, Béliveau, J. J. Van Van Hoecke, C. Garapon-Bar, E. Gaillard, J. I P. P.Herry, Herry, G. G. Atlan Atlan and and P. P. Bouissou, Bouissou, MyoelecFatigue. trical and Metabolic MetabolicChanges ChangesininMuscle Muscle Fatigue.Int IntJJ trical and SportsMed,Vo113,Suppll,ppSl53—S155,1992. SportsMed,Vol 13,Suppl 1,ppSl53—S!55, 1992.
In isometric isometriccontraction-induced contraction-induced fatigue fatigue In
force loss has been related to mostly myoelectrical or intramuscular events. However, some factors potentially involved may interfere at more than one site in these events and it has proven difficult difficult to to distinguish distinguish between between those thoseininfluences. The study of the relationships between force generating capacity, the metabolic state of a muscle and its myoelectrical properties may therefore help broaden our understanding of the fatigue fatigue process. process. In In order order to to investigate investigate these relationships, we have evaluated changes in forcegenerating capacity, NMR-determined metabolic variables, and myoelectrical activity, as measured from surface EMG, simultaneously in brachial biceps muscle of healthy subjects, during different types of fatiguing isometric exer-
cise and during recovery. Factors studied include intramuscular pH, inorganic phosphate and its diprotonated form concentrations, root-mean square and mean power frequency of the EMG power spectrum, and neuromuscular efficiency index. Results show that different mecha-
nisms are likely to contribute to force loss in fatiguing muscle and during different phases of recovery from fatigue. Indeed, relationships between variables from the three groups differed according to exercise protocol as well as in fatiguing and recovering muscle. Key words
Muscle, electromyography, nuclear magnetic resonance, fatigue, intramuscular pH
recorded changes recent studies, in which we we simultaneously simultaneousy recorded in surface electromyography electromyography (EMG) (EMG) and and 1P-nuclear magnetic resonance (NMR) spectroscopy data from brachial biceps
of healthy subjects during continuous or intermittent isometric contractions at 30 or 70% of maximal voluntary contaction (MVC) and during recovery.
1. Relationship between Spectral Shift of the EMG Power Spectrum and Metabolic Variables
The mechanisms causing the well-known changes of the frequency components components of of the the EMG EMG power power spectrum during fatigue have not been clearly identified. It has
been suggested that intramuscular accumulation of protons might might be be responsible responsible for for the the decrease decrease in in muscle muscle fiber fiber conducconduction velocity (8) that is associated in many studies to EMG power spectrum changes (3, 11). However, although a correlative relationship has been reported between pH and myoelec4, 5, 5, trical signal spectral parameters, parameters, there there are are exceptions exceptions (1, (1,4, 7). Indeed, using EMG and muscle biopsies, Bouissou et al. (4)
have observed a correlation between mean power frequency (MPF) of the EMG power spectrum and intramuscular lactate concentration, but no relationship with muscle pH during dynamic exercise in man. Furthermore, different behaviors of myoelectrical signal spectral parameters and pH have been described during recovery from fatiguing contractions. This discrepancy could have been related to the difficulty of obtaining accurate measurements of cytosolic pH. We have therefore reexamined this relationship, using NMR spectroscopy, in the during an an isometric isometric contraction contractionatat30 30% human brachial biceps during % of MVC performed until fatigue and during recovery of recovery (1). (1). ReResults show that if during fatiguing contraction the decrease in
MPF did appear to follow a pattern similar to that of the decrease in muscle pH, those variables were completely disso-
ciated during recovery (Figure 1). MPF was completely recovered within a few minutes, despite the persistence of acido-
sis (1). Those results are in line with recent observations by Brody et al. (5) in an in vitro vitro preparation preparation of ofhamster hamster muscle dia-
phragm strips. They have reported a relationship between changes in bath pH and initial conduction velocity and surIntroduction
Analysis of the surface-detected myoelectrical the study of localized muscle fatigue. signal is often used in the Metabolic factors have been speculated to influence myoelectrical changes associated with fatigue (2, 5, 8). However, the relationships between those factors have not been clearly estab-
lished. This paper focuses on some of these relationships, reviewing some related literature and reporting results from our Int.J.SportsMed. 13(1992)S153—S155 Georglhieme Verlag New York Georglhieme VerlagStuttgart StuttgartNewYork
face-detected median frequency (MDF). In contrast, conduction velocity and the decay in MDF were altered differently
during stimulated sustained contractions. Taken together, these observations indicate that the change in the frequency components of the EMG power spectrum is not uniquely determined by a change in muscle pH and conduction velocity. Other mechanisms, either central or peripheral, must therefore intervene. Other metabolites that have been the subject of
interest in the study of muscle fatigue include inorganic phosphate (Pi) and its diprotonated form H2PO4 We have observed an associative relationship between H2PO4 ob-
Downloaded by: Queen's University. Copyrighted material.
Abstract
S154 mt. I Sports Med. 13(1992)
L. Béliveau, J. Van Hoecke, C. Garapon-Bar, E. Gaillard, J. P. Herry eta!. et al.
2. Relationship between Amplitude of the EMG Power spectrum and Metabolic Variables
The increase in electrical activity observed during fatiguing exercise can be related to motor unit recruitment and motor unit synchronization (6) as shown in Table 1, root-mean square of the EMG power spectrum, reflecting its amplitude, increases in relation to workload. During recovery from fatiguing continuous or intermittent isometric contraction of the brachial biceps, recuperation of force and RMS are much faster than that of intramuscular metabolites measured
using NMR, although force had not completely recovered after 5 mm (Table 1). This confirms that delayed recovery of force-generating capacity following isometric exercise is caused by caused by processes processeswithin withinthe themuscle muscleitself(1O). itself(l0).
The ratio of force to RMS during contraction
can be viewed as an index of neuromuscular efficiency efficiency (NME), as a decrease in this ratio would imply that more electrical activity is needed to produce the same force. This ratio was decreased immediately immediately after after fatiguing fatiguing isometric isometric exercise exercise
in the brachial biceps. However, it recovered very rapidly, thus indicating the absence of excitation-contraction uncoupling in these conditions. Recovery of the NME index was not parallel to recoveries of force or RMS, which were slower. This observation supports the hypothesis, as first suggested by BiglandRitchie et al. (2), of adaptability of motor command to the level
of force the muscle can develop. Motoneurones firing rates could indeed be modulated to optimize force generation as muscle properties change with recovery. This modulation could arise from a reflex originating within the muscle (2). Fatigue-induced changes in muscle contractile properties, as transmitted from muscle spindles or Golgi tendon organs, or in metabolic variables, detected via chemosensitive afferents in the proximity of muscle fibers, could be the connecting link between status of the muscle and command. Intramuscular accumulation of ofprotons protons may may serve serve as as this this metabolic link. For instance, Table 1 shows that much higher proton accumulation
during continuous isometric contraction was paralleled by a lower increase in RMS at fatigue, hinting at the possibility of an inhibition of motoneurone firing rates. However, the rapidity of RMS recuperation with respect to that of intramuscular pH during the first minutes of recovery suggests pH could not be a unique determinant of this phenomenon. Changes in intracellular Pi, PCr and H2P04 concentrations did appear to follow changes in RMS during recovery. However, causal relationships lationships are difficult to establish under such conditions. conditions. Acknowledgements
MVC
110. 1iO
- 7.2 7.2
100. 1oo of initial) initial) (% of (%
•• 7.0 7.0
MW
P11
These studies were supported by the Laboratoire de Recherches Pharmaceutiques Sandoz France. L. Béliveau was a Natural Science and Engineering Research Council of Canada post-doepost-doctoral toral fellow.
References
9O 90.
1
6.8
so. 80. • 6.6 6.6
Béliveau Béliveau L., L., Helal Helal J. N., Gaillard E. E. Van Van Hoecke HoeckeJ., J.,Atlan AtlanG., G., Bouissou P.: EMG spectral shift and 1PNMRdetermined intracellular pH in fatigued human biceps brachii muscle. Neurology
2 41:1998—2001,1991.
70. 70
B., Dawson N. J., Johansson R. S., Lippokl Lippold 0. C. J.: Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary 379: 451—459, voluntary contractions. contractions. JPhysiol JPhysiol379: Bigland-Ritchie
• 6.4
60
1986.
Bigland-Ritchie B., Donovan F. E. F., Roussos C. S.: Conduction 50
I Rest
I
Fatigue
velocity and EMG power spectrum changes in fatigue of sustained maximalefforts.JApplPhysiol5l: maximal efforts.JAppl Physiol5l: 1300—1305,1981. 1300—1305,1981. Bouissou P., Estrade P. Y., Goubel F., Guezennec C. Y., Serrurier B.: Surface EMG power spectrum and intramuscular pH in vastus lateralis muscle during during dynamic dynamic exercise. exercise. JAppI JAppi Physiol Physiol 67: 67:1245— 1245— 1249, 1989.
6.2
(miii) Recovery (mm) Recovery
3
1
5
Changesininmean meanpower powerfrequency frequency(MPF), (MPF),maximal maximal volunvolunFig. 1 Changes tary contraction (MVC) and pH during exercise and recovery.
Table I Mycelectrical by 30% 30% MVC MVC continuous aand Myoelectrical and metabolic changes induced by nd by 70% MVC in termittent exercise. Rest
300/o continuous exercise 30% continuous exercise
RI
F Workload
100
71
74
100
65
106
a
81
a
86
70% 700/o intermitten intermitten t exercise Ri RI R3
F
R5 ff5
R3
a
73 73
a
R5
80
85
88
106
95
95
a
(% MVC) RMS (% max) pH
H2P04
713±03 100
a
2357
91
6.50±13 6.50±13 a
6.37±.O 6.37±06
6.34±10 2920
95
a
1546
a
6.68±08 848
95
b.C b.c
6.66±05 a,b 3097
651±06 a 6.51±06
6.41±08 2618
'F: F: fatigue, fatigue, Al, Ri, ff3, R3, R5: R5: first, first, third third and and titth fifth minute of recovery. 'significantly different asignltlcantly differentfrom fromrest: rest;5significantly bsignilicantlydifferent differentfrom fromow-intensity ow-intensitycontinuous continuousexercise; exercise;°significantly Csigflificantlydifferent differentfrom fromstart startofoffatiguing fatiguing exercise exercise(F1MS). (RMS).
a
1808
a
6.62±05 a 830
a
Downloaded by: Queen's University. Copyrighted material.
tamed from NMR-determined Pi measurements and a pK of 6.75 for phosphoric acid. Portero et al. at. (9) have recently reported a similar relationship, and suggested this link might be related to fiber type recuitment.
mt. J. Sports Med. 13(1992) S155
Myoelectrical and Metabolic Changes in Muscle Fatigue Brody L. R., Pollock M. T., Roy S. H., De Luca C. J., Celli B.: pH-
induced effects on median frequency and conduction velocity of myoelectric signal. signal.JApplPhysiol7l: 1878—1885,1991. myoelectric JApplPhysiol7l: 1878—1885, 1991. 6 the Luca C. J.: Myoelectrical manifestations of localized muscular De fatigue in humans. CRC CritRevBiomedEng11:251—279, 11:251—279,1984. 1984. CRCCritRevBiomedEng Mills K. R., Edwards R. H. T.: Muscle fatigue in myophosphory-
lase electromyogram. lase deficiency: power spectral analysis of the electromyogram.
10 10
Sahlin K., Ren J. M.: Relationship of of contraction contraction capacity to meM. Relationship
tabolic changes during recovery from a fatiguing contraction. J ApplPhysiol67: 648—654,1989. ApplPhysiol67:648—654, 1989.
Zwarts M. M. J., J., Van Van Weereden Weereden T. T. W., W., Haenen Haenen T. T. M.: M.: Relationship Relationship Zwarts
between average muscle fiber conduction velocity between velocity and and EMG EMG power spectra during isometric contraction, recovery, and applied ischemia.EurJApplPhysiolOccupPhysiols6:212—216, ischemia. EurJApplPhysiol Occup Physiol 56:212—216, 1987.
Electroencephalogr Clin Clin Neurophysiol57: Neurophysiols7: 330—335, 330—335, 1984. 1984.
8
Mortimer J. T., Magnusson P., Petersen I.: Conduction velocity in ischemic muscle: effect on EMG frequency spectrum. Am J Phys- Dr. Louise Béliveau JPhys-
Portero P., Laurent D., Rossi Rossi A., A., Goubel Goubel F.: F.: Human Human muscle muscle fatigue studied by electromyography and 31P-NMR spectroscopy. IntJSports Med 13: 85, 85, 1992. 1992. IntJSportsMedl3:
Département d'Education Physique Département Université de de Montréal Montréal Université C. P.6128,Succ.A C. Montréal, Québec Québec Montréal, Canada H3C H3C 3J7 3J7 Canada
Metabolic Transient Studies by NMR T Binzoni1'4, G. Ferretti1 , K. Schenker2 , F. Barbalat3 , E. Hiltbrand4 , P. Cerreteii1 'Dept. de Physiologic, CMU, Genève, Switzerland 2Spectrospin AG, Fãllanden, Switzerland 3Dépt. de Chimie Pharmaceutique, Faculté des Sciences, Genève, Switzerland 4Dépt. de Radiologie, HCUG, Genève, Switzerland
Abstract
T Binzoni, G. Ferretti, K. Schenker, F. Barbalat, E. Hiltbrand and P. Cerretelli, Metabolic Transient Studies by NMR. Tnt J Sports Med, Vol 13, Suppl 1, pp Si 55—S 157,1992.
The time course of phosphocreatine (PC) hydrolysis in humans was measured by 31P-NMR spectroscopy (31P-NMRS) with a time resolution of 10.8 s in the gastrocnemius muscle and a relationship between muscle 02 consumption (V02) and [PC] was derived from a bioenergetic model. This allowed a direct estimate of the halftime of the intracellular V02 kinetics (ti /2V02) of the con-
tracting human gastrocnemius in aerobic conditions.
Introduction
During metabolic transients the aerobic and anaerobic (glycolytic and alactic) energetic reactions contrib-
ute to a variable extent to the resynthesis of adenosine tnphosphate (ATP) (4). The relative role of each of the above exoergonic processes can be established only if their kinetics is Int.J.SportsMed. 13(1992)S155—S157 GeorgThieme Verlag Stuttgart New York
tl/2 V02 was found to be — 16 s and independent of the work load. This value corresponds to the shortest tl/2V02 determined at the mouth of the subject in the absence of lac-
tate accumulation in the rest to work transient. tl/2V02 may now be assessed in man at low muscle temperatures. To this aim a procedure was developed allowing corrections of the 31P-NMR spectra based on the muscle temperature profiles obtained by a simultaneously acquired proton image. Key words
Exercise, phosphocreatine, 02 consumption, temperature, muscle, 31P-NMR, humans
determined directly in the cells. Indeed, indirect markers such as 02 and C02 exchange for the oxidative processes and lactate production for anaerobic glycolysis are usually delayed and cannot reflect faithfully the time course of the readjustment of the investigated energy yielding processes. In addition, the interplay among the above mentioned energy sources
may be greatly affected by environmental and/or physicochemical variables depending on physiological and/or artificially induced conditions, such as hypo- and hyperthermia, hypoxia, alteration of the acid-base balance, etc.
Downloaded by: Queen's University. Copyrighted material.
io1219: 1324—1329,1970.
Myoelectrical and Metabolic Changes in Muscle Fatigue L. Béliveau, Béliveau, J. J. Van Van Hoecke, Hoecke,C. C.Garapon-Bar, Garapon-Bar,E,E.Gaillard, Gaillard,J.I P. P.Herry, Herry,G. G.Atlan, Atlan,P.P.Bouissou Bouissou Laboratoire RMN, Hôpital de Chamonix, Charnonix, Chamoriix, Chamonix, and INSEP, Paris, France
L. Be'liveau, Béliveau, J. J. Van Van Hoecke, C. Garapon-Bar, E. Gaillard, J. I P. P.Herry, Herry, G. G. Atlan Atlan and and P. P. Bouissou, Bouissou, MyoelecFatigue. trical and Metabolic MetabolicChanges ChangesininMuscle Muscle Fatigue.Int IntJJ trical and SportsMed,Vo113,Suppll,ppSl53—S155,1992. SportsMed,Vol 13,Suppl 1,ppSl53—S!55, 1992.
In isometric isometriccontraction-induced contraction-induced fatigue fatigue In
force loss has been related to mostly myoelectrical or intramuscular events. However, some factors potentially involved may interfere at more than one site in these events and it has proven difficult difficult to to distinguish distinguish between between those thoseininfluences. The study of the relationships between force generating capacity, the metabolic state of a muscle and its myoelectrical properties may therefore help broaden our understanding of the fatigue fatigue process. process. In In order order to to investigate investigate these relationships, we have evaluated changes in forcegenerating capacity, NMR-determined metabolic variables, and myoelectrical activity, as measured from surface EMG, simultaneously in brachial biceps muscle of healthy subjects, during different types of fatiguing isometric exer-
cise and during recovery. Factors studied include intramuscular pH, inorganic phosphate and its diprotonated form concentrations, root-mean square and mean power frequency of the EMG power spectrum, and neuromuscular efficiency index. Results show that different mecha-
nisms are likely to contribute to force loss in fatiguing muscle and during different phases of recovery from fatigue. Indeed, relationships between variables from the three groups differed according to exercise protocol as well as in fatiguing and recovering muscle. Key words
Muscle, electromyography, nuclear magnetic resonance, fatigue, intramuscular pH
recorded changes recent studies, in which we we simultaneously simultaneousy recorded in surface electromyography electromyography (EMG) (EMG) and and 1P-nuclear magnetic resonance (NMR) spectroscopy data from brachial biceps
of healthy subjects during continuous or intermittent isometric contractions at 30 or 70% of maximal voluntary contaction (MVC) and during recovery.
1. Relationship between Spectral Shift of the EMG Power Spectrum and Metabolic Variables
The mechanisms causing the well-known changes of the frequency components components of of the the EMG EMG power power spectrum during fatigue have not been clearly identified. It has
been suggested that intramuscular accumulation of protons might might be be responsible responsible for for the the decrease decrease in in muscle muscle fiber fiber conducconduction velocity (8) that is associated in many studies to EMG power spectrum changes (3, 11). However, although a correlative relationship has been reported between pH and myoelec4, 5, 5, trical signal spectral parameters, parameters, there there are are exceptions exceptions (1, (1,4, 7). Indeed, using EMG and muscle biopsies, Bouissou et al. (4)
have observed a correlation between mean power frequency (MPF) of the EMG power spectrum and intramuscular lactate concentration, but no relationship with muscle pH during dynamic exercise in man. Furthermore, different behaviors of myoelectrical signal spectral parameters and pH have been described during recovery from fatiguing contractions. This discrepancy could have been related to the difficulty of obtaining accurate measurements of cytosolic pH. We have therefore reexamined this relationship, using NMR spectroscopy, in the during an an isometric isometric contraction contractionatat30 30% human brachial biceps during % of MVC performed until fatigue and during recovery of recovery (1). (1). ReResults show that if during fatiguing contraction the decrease in
MPF did appear to follow a pattern similar to that of the decrease in muscle pH, those variables were completely disso-
ciated during recovery (Figure 1). MPF was completely recovered within a few minutes, despite the persistence of acido-
sis (1). Those results are in line with recent observations by Brody et al. (5) in an in vitro vitro preparation preparation of ofhamster hamster muscle dia-
phragm strips. They have reported a relationship between changes in bath pH and initial conduction velocity and surIntroduction
Analysis of the surface-detected myoelectrical the study of localized muscle fatigue. signal is often used in the Metabolic factors have been speculated to influence myoelectrical changes associated with fatigue (2, 5, 8). However, the relationships between those factors have not been clearly estab-
lished. This paper focuses on some of these relationships, reviewing some related literature and reporting results from our Int.J.SportsMed. 13(1992)S153—S155 Georglhieme Verlag New York Georglhieme VerlagStuttgart StuttgartNewYork
face-detected median frequency (MDF). In contrast, conduction velocity and the decay in MDF were altered differently
during stimulated sustained contractions. Taken together, these observations indicate that the change in the frequency components of the EMG power spectrum is not uniquely determined by a change in muscle pH and conduction velocity. Other mechanisms, either central or peripheral, must therefore intervene. Other metabolites that have been the subject of
interest in the study of muscle fatigue include inorganic phosphate (Pi) and its diprotonated form H2PO4 We have observed an associative relationship between H2PO4 ob-
Downloaded by: Queen's University. Copyrighted material.
Abstract
S154 mt. I Sports Med. 13(1992)
L. Béliveau, J. Van Hoecke, C. Garapon-Bar, E. Gaillard, J. P. Herry eta!. et al.
2. Relationship between Amplitude of the EMG Power spectrum and Metabolic Variables
The increase in electrical activity observed during fatiguing exercise can be related to motor unit recruitment and motor unit synchronization (6) as shown in Table 1, root-mean square of the EMG power spectrum, reflecting its amplitude, increases in relation to workload. During recovery from fatiguing continuous or intermittent isometric contraction of the brachial biceps, recuperation of force and RMS are much faster than that of intramuscular metabolites measured
using NMR, although force had not completely recovered after 5 mm (Table 1). This confirms that delayed recovery of force-generating capacity following isometric exercise is caused by caused by processes processeswithin withinthe themuscle muscleitself(1O). itself(l0).
The ratio of force to RMS during contraction
can be viewed as an index of neuromuscular efficiency efficiency (NME), as a decrease in this ratio would imply that more electrical activity is needed to produce the same force. This ratio was decreased immediately immediately after after fatiguing fatiguing isometric isometric exercise exercise
in the brachial biceps. However, it recovered very rapidly, thus indicating the absence of excitation-contraction uncoupling in these conditions. Recovery of the NME index was not parallel to recoveries of force or RMS, which were slower. This observation supports the hypothesis, as first suggested by BiglandRitchie et al. (2), of adaptability of motor command to the level
of force the muscle can develop. Motoneurones firing rates could indeed be modulated to optimize force generation as muscle properties change with recovery. This modulation could arise from a reflex originating within the muscle (2). Fatigue-induced changes in muscle contractile properties, as transmitted from muscle spindles or Golgi tendon organs, or in metabolic variables, detected via chemosensitive afferents in the proximity of muscle fibers, could be the connecting link between status of the muscle and command. Intramuscular accumulation of ofprotons protons may may serve serve as as this this metabolic link. For instance, Table 1 shows that much higher proton accumulation
during continuous isometric contraction was paralleled by a lower increase in RMS at fatigue, hinting at the possibility of an inhibition of motoneurone firing rates. However, the rapidity of RMS recuperation with respect to that of intramuscular pH during the first minutes of recovery suggests pH could not be a unique determinant of this phenomenon. Changes in intracellular Pi, PCr and H2P04 concentrations did appear to follow changes in RMS during recovery. However, causal relationships lationships are difficult to establish under such conditions. conditions. Acknowledgements
MVC
110. 1iO
- 7.2 7.2
100. 1oo of initial) initial) (% of (%
•• 7.0 7.0
MW
P11
These studies were supported by the Laboratoire de Recherches Pharmaceutiques Sandoz France. L. Béliveau was a Natural Science and Engineering Research Council of Canada post-doepost-doctoral toral fellow.
References
9O 90.
1
6.8
so. 80. • 6.6 6.6
Béliveau Béliveau L., L., Helal Helal J. N., Gaillard E. E. Van Van Hoecke HoeckeJ., J.,Atlan AtlanG., G., Bouissou P.: EMG spectral shift and 1PNMRdetermined intracellular pH in fatigued human biceps brachii muscle. Neurology
2 41:1998—2001,1991.
70. 70
B., Dawson N. J., Johansson R. S., Lippokl Lippold 0. C. J.: Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary 379: 451—459, voluntary contractions. contractions. JPhysiol JPhysiol379: Bigland-Ritchie
• 6.4
60
1986.
Bigland-Ritchie B., Donovan F. E. F., Roussos C. S.: Conduction 50
I Rest
I
Fatigue
velocity and EMG power spectrum changes in fatigue of sustained maximalefforts.JApplPhysiol5l: maximal efforts.JAppl Physiol5l: 1300—1305,1981. 1300—1305,1981. Bouissou P., Estrade P. Y., Goubel F., Guezennec C. Y., Serrurier B.: Surface EMG power spectrum and intramuscular pH in vastus lateralis muscle during during dynamic dynamic exercise. exercise. JAppI JAppi Physiol Physiol 67: 67:1245— 1245— 1249, 1989.
6.2
(miii) Recovery (mm) Recovery
3
1
5
Changesininmean meanpower powerfrequency frequency(MPF), (MPF),maximal maximal volunvolunFig. 1 Changes tary contraction (MVC) and pH during exercise and recovery.
Table I Mycelectrical by 30% 30% MVC MVC continuous aand Myoelectrical and metabolic changes induced by nd by 70% MVC in termittent exercise. Rest
300/o continuous exercise 30% continuous exercise
RI
F Workload
100
71
74
100
65
106
a
81
a
86
70% 700/o intermitten intermitten t exercise Ri RI R3
F
R5 ff5
R3
a
73 73
a
R5
80
85
88
106
95
95
a
(% MVC) RMS (% max) pH
H2P04
713±03 100
a
2357
91
6.50±13 6.50±13 a
6.37±.O 6.37±06
6.34±10 2920
95
a
1546
a
6.68±08 848
95
b.C b.c
6.66±05 a,b 3097
651±06 a 6.51±06
6.41±08 2618
'F: F: fatigue, fatigue, Al, Ri, ff3, R3, R5: R5: first, first, third third and and titth fifth minute of recovery. 'significantly different asignltlcantly differentfrom fromrest: rest;5significantly bsignilicantlydifferent differentfrom fromow-intensity ow-intensitycontinuous continuousexercise; exercise;°significantly Csigflificantlydifferent differentfrom fromstart startofoffatiguing fatiguing exercise exercise(F1MS). (RMS).
a
1808
a
6.62±05 a 830
a
Downloaded by: Queen's University. Copyrighted material.
tamed from NMR-determined Pi measurements and a pK of 6.75 for phosphoric acid. Portero et al. at. (9) have recently reported a similar relationship, and suggested this link might be related to fiber type recuitment.
mt. J. Sports Med. 13(1992) S155
Myoelectrical and Metabolic Changes in Muscle Fatigue Brody L. R., Pollock M. T., Roy S. H., De Luca C. J., Celli B.: pH-
induced effects on median frequency and conduction velocity of myoelectric signal. signal.JApplPhysiol7l: 1878—1885,1991. myoelectric JApplPhysiol7l: 1878—1885, 1991. 6 the Luca C. J.: Myoelectrical manifestations of localized muscular De fatigue in humans. CRC CritRevBiomedEng11:251—279, 11:251—279,1984. 1984. CRCCritRevBiomedEng Mills K. R., Edwards R. H. T.: Muscle fatigue in myophosphory-
lase electromyogram. lase deficiency: power spectral analysis of the electromyogram.
10 10
Sahlin K., Ren J. M.: Relationship of of contraction contraction capacity to meM. Relationship
tabolic changes during recovery from a fatiguing contraction. J ApplPhysiol67: 648—654,1989. ApplPhysiol67:648—654, 1989.
Zwarts M. M. J., J., Van Van Weereden Weereden T. T. W., W., Haenen Haenen T. T. M.: M.: Relationship Relationship Zwarts
between average muscle fiber conduction velocity between velocity and and EMG EMG power spectra during isometric contraction, recovery, and applied ischemia.EurJApplPhysiolOccupPhysiols6:212—216, ischemia. EurJApplPhysiol Occup Physiol 56:212—216, 1987.
Electroencephalogr Clin Clin Neurophysiol57: Neurophysiols7: 330—335, 330—335, 1984. 1984.
8
Mortimer J. T., Magnusson P., Petersen I.: Conduction velocity in ischemic muscle: effect on EMG frequency spectrum. Am J Phys- Dr. Louise Béliveau JPhys-
Portero P., Laurent D., Rossi Rossi A., A., Goubel Goubel F.: F.: Human Human muscle muscle fatigue studied by electromyography and 31P-NMR spectroscopy. IntJSports Med 13: 85, 85, 1992. 1992. IntJSportsMedl3:
Département d'Education Physique Département Université de de Montréal Montréal Université C. P.6128,Succ.A C. Montréal, Québec Québec Montréal, Canada H3C H3C 3J7 3J7 Canada
Metabolic Transient Studies by NMR T Binzoni1'4, G. Ferretti1 , K. Schenker2 , F. Barbalat3 , E. Hiltbrand4 , P. Cerreteii1 'Dept. de Physiologic, CMU, Genève, Switzerland 2Spectrospin AG, Fãllanden, Switzerland 3Dépt. de Chimie Pharmaceutique, Faculté des Sciences, Genève, Switzerland 4Dépt. de Radiologie, HCUG, Genève, Switzerland
Abstract
T Binzoni, G. Ferretti, K. Schenker, F. Barbalat, E. Hiltbrand and P. Cerretelli, Metabolic Transient Studies by NMR. Tnt J Sports Med, Vol 13, Suppl 1, pp Si 55—S 157,1992.
The time course of phosphocreatine (PC) hydrolysis in humans was measured by 31P-NMR spectroscopy (31P-NMRS) with a time resolution of 10.8 s in the gastrocnemius muscle and a relationship between muscle 02 consumption (V02) and [PC] was derived from a bioenergetic model. This allowed a direct estimate of the halftime of the intracellular V02 kinetics (ti /2V02) of the con-
tracting human gastrocnemius in aerobic conditions.
Introduction
During metabolic transients the aerobic and anaerobic (glycolytic and alactic) energetic reactions contrib-
ute to a variable extent to the resynthesis of adenosine tnphosphate (ATP) (4). The relative role of each of the above exoergonic processes can be established only if their kinetics is Int.J.SportsMed. 13(1992)S155—S157 GeorgThieme Verlag Stuttgart New York
tl/2 V02 was found to be — 16 s and independent of the work load. This value corresponds to the shortest tl/2V02 determined at the mouth of the subject in the absence of lac-
tate accumulation in the rest to work transient. tl/2V02 may now be assessed in man at low muscle temperatures. To this aim a procedure was developed allowing corrections of the 31P-NMR spectra based on the muscle temperature profiles obtained by a simultaneously acquired proton image. Key words
Exercise, phosphocreatine, 02 consumption, temperature, muscle, 31P-NMR, humans
determined directly in the cells. Indeed, indirect markers such as 02 and C02 exchange for the oxidative processes and lactate production for anaerobic glycolysis are usually delayed and cannot reflect faithfully the time course of the readjustment of the investigated energy yielding processes. In addition, the interplay among the above mentioned energy sources
may be greatly affected by environmental and/or physicochemical variables depending on physiological and/or artificially induced conditions, such as hypo- and hyperthermia, hypoxia, alteration of the acid-base balance, etc.
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