Acta physiol. scand. 1975. 93.135-138 From the Department of Physiology, Gymnastik- och idrottshogskolan, Stockholm, Sweden
Relationship between Isometric Endurance and Fibre Types in Human Leg Muscles BY
B. H U L T ~ NA. , THORSTENSSON, B. SJODINand J. KARLSSON Received 19 July 1974
Abstract HULTBN,B., A. THORSTENSSON, B. SJODINand J. KARLSSON. Relationship between isometric endurance and fibre types in human leg muscles. Acta physiol. scand. 1975. 93. 135-1 38. Relationship between isometric endurance performance at 50% of maximal voluntary isometric contraction (MVC)and skeletal muscle fibre composition has been elucidated in 19 physical education students. This was found to be linear and the equation corresponded to: y = 9 . 3 5 f 1.093~;r=0.70 (endurance time expressed in seconds and fibre composition as percent slow twitch muscle fibres (ST) of the vastus lateralis muscle). As it is assumed from previous studies that similar isometric tensions preferentially recruit fast twitch muscle fibres (FT) and that the muscle at the point of exhaustion exhibits maximal values for lactate accumulation, it is suggested that lactate formed in F T fibres is released and stored in nonrecruited S T fibres. The ability to sustain similar isometric tension would then be depending on how large the fraction of ST fibres is that can serve as a lactate recipient for lactate producing FT fibres.
Isometric tensions corresponding to 30-50% of maximal leg voluntary isometric contraction (MVC) have been shown to produce maximal values for muscle lactate concentrations a t the point of muscular exhaustion (Karlsson and Ollander 1972, Karlsson et al. 1974). Lower and higher relative tensions, respectively, were demonstrated to cause submaximal phosphagen depletions as well as submaximal lactate accumulations in spite of muscular exhaustion. Repeated exhaustive isometric contractions at tensions corresponding to 30-80% of MVC did not change the metabolic pattern obtained after the first contraction; no further accumulation of lactate did occur (Karlsson er al. 1974). Furthermore, it has been demonstrated that at isometric tensions corresponding to approximately 25 % of MVC or less only slow twitch fibres (ST) were depleted on their glycogen content, as indicated by periodic acid Schiff (PAS) stainings (Gollnick el al. 1974). At tensions in excess of 25% only the fast twitch fibres (FT) were glycogen depleted. The interpretation was, that only FT were recruited to maintain high tensions, whereas at lower tensions only ST were recruited. This conclusion about the recruitment pattern seemed to be in contradiction to results from Molbech et al. (1973), who investigated isometric endurance in muscles with different contractile characteristics and consequently, most likely, with different fibre 135
I36
B. H U L T ~ N ,A. THORSTENSSON, B. SJODIN AND J . KARLSSON
populations. They showed that isometric endurance time at 50% of MVC was longer for muscles with predominantly slow twitch characteristics than for muscles with predominantly fast twitch properties. To further investigate how fibre composition is related to isometric endurance, 19 subjects were examined at a tension corresponding to 50% of MVC, and muscle biopsies were obtained for fibre-typing. It was demonstrated that isometric endurance at this intensity was positively correlated to the percentage of slow twitch fibres.
Methods 19 students of physical education participated in the study. For antropological and physiological data, see Table I. The experiments were performed in an isometric chair, as described by Karlsson and Ollander (1972) by pressing the feet against an immovable bar whereby activating mainly the thigh muscles. MVC was determined on 2 consecutive days and from these data individual tensions corresponding to 50% of MVC were calculated. The endurance tests were performed on the third day. The subjects reported
in the laboratory early in the morning after a light breakfast and the experiments were performed without any preceding maximal tests. Muscle biopsies (Bergstrom 1962) were obtained from vastus lateralis on one of the first two days and analyzed for fibre types according to Gollnick e r a/. (1972).
Results and Discussion Individual MVC ranged 195-400 kp (mean 245 kp) and fibre composition 38-69?/, ST (mean 54% ST) for the experimental group (Table I). No relationship was found between individual MVC and fibre type composition. Endurance time at 50% MVC ranged 56-94 sec and was related to the individual fibre type composition (Fig. I), demonstrating an increased performance with a higher percentage ST fibres. These findings are in accordance with the conclusions of Molbech et af. (1973), that endurance is related to the quality of the muscle with respect to fibre type composition. A previous study suggested that isometric tensions in excess of approximately 25 % of MVC are produced by the recruitment of FT fibres (Gollnick et af. 1974). However, in the present study maximal tensions could not be related to the percentage FT fibres indicating additional factors of significance for peak tension. Since blood flow at tensions corresponding to 50% MVC are severely restricted with n o or very little oxygen delivery to the contracting fibres (for further discussion see Eklund 1974), the anaerobic glycolysis will be utilized for ATP resynthesis (Karlsson 1971). Lactate will then accumulate in the fibres and be released into the extra-cellular fluid and the venous blood. Since venous lactate efflux from contracting muscle already during conditions similar to dynamic exercise has been shown to be limited (Karlsson 1971 and TABLE 1. Mean va1ueskS.E. for age, weight, height, maximal isometric tension (MVC), and percent slow twitch fibres (ST) of the examined muscle (vastus lateralis).
Number of subjects
Age years
Weight kg
Height cm
MVC kp
%, S T
Fibre composition
n - 19
24k0.8
74.2+ 3.1
179+2
245+ 14
54+9
I37
ISOMETRIC ENDURANCE AND MUSCLE FIBRE TYPES
90 t-
100
0 0
80 0
70 -
60-
50-
y 9 45*10'~~X
40 -
r - 070
0
0
304
1
'
40
50 % of slow twitch
60
70
hbers
Fig. 1. Relationship between individual endurance time and percent slow twitch fibres of the examined muscle (vastus lateralis).
Jorfeldt pers. corn.), the rate of lactate accumulation in the contracting muscle during isometric exercise will most probably be much more pronounced as compared to dynamic exercise. The lactate anion in itself has been demonstrated to be a potent inhibitor of lactate formation during in vitro conditions (Karlsson, Hult6n and Sjodin 1974). If this is true also in situ, it seems reasonable to assume a subsequent arrest of the glycolysis at peak values of lactate accumulation due to the fact that the whole extramitochondrial pool of N A D will be transferred into a reduced form (Sund 1968). If so, the release of lactate to other compartments than the venous blood ought to be detrimental for the capability of the muscle to sustain an isometric contraction. Nonrecruited ST fibres is one very probable recipient of released lactate. In addition ST fibres might be able to metabolize lactate formed in FT fibres. The prerequisites for lactate oxidation in skeletal muscle in terms of the heart specific LDH isozymes are present in ST fibres (Karlsson et al. 1974). Moreover, ST fibres have been shown to contain larger amounts of myoglobin than FT fibres (James 1968).
References BERGSTRBM, J . Muscle electrolytes in man. Srand. J. din. Lab. Inrest. 1962. Suppl. 68. EKLUND,B. lnfluence of work duration on the regulation of muscle blood flow. Artu physiol. scand. 1974. Suppl. 411. GOLLNICK, P. D., R. B. ARMSTRONG, C. W. SAUBERT IV, K . PIEHL,B. SALTIN.Enzyme activity and fiber composition in skeletal muscle of untrained and trained men. J. uppl. Physiol. 1972. 33. 312-319. GOLLNICK, P. D., B. SIBDIN,J. KARLSSON, E. JANSSON and B. SALTIN. Human Soleus Muscle: A comparison of fiber composition and enzyme activities with other leg muscles. Pflugers Arch. gus. Physiol. 1974348. 247-255.
138
B.
HULTEN,
A. THORSTENSSON, B. S J ~ D I NAND J. KARLSSON
JAMES,N. T. Histochemical demonstration of myoglobin in skeletal muscle fibres and muscle spindles. Nature (Lond.) 1968. 219. 1174-1 175. KARLSSON, J. Lactate and phosphagen concentrations in working muscle of man. Acru physiol. scand. 1971. Suppl. 358. KARLSSON, J. and B. OLLANDER. Muscle metabolites with exhaustive static exercise of different duration. Arta physiol. scand. 1972. 86. 309-314. KARLSSON, J., B. H U L T ~ Nand B. SIBDIN.Substrate activation and product inhibition of LDH activity in human skeletal muscle. Acta physiol. scand. 1974. 92. 21-26. KARLSSON, J., C. F. FUNDERBURK, B. ESSLNand A. R. LIND.Constituents of human muscle in isometric fatigue. J . appl. Physiol. 1974. In press. MOLBECH, S. and S. H. JOHANSEN. Endurance time in slow and fast contracting muscle groups. Worki~nrironnr.-hlth.1973. 10. 62-64. SUND, H. The pyridine nucleotide coenzymes. In Biological oxidations, ed. T. P . Singer. Interscience Publ. New York. 1968. 603-639.
Relationship between Isometric Endurance and Fibre Types in Human Leg Muscles BY
B. H U L T ~ NA. , THORSTENSSON, B. SJODINand J. KARLSSON Received 19 July 1974
Abstract HULTBN,B., A. THORSTENSSON, B. SJODINand J. KARLSSON. Relationship between isometric endurance and fibre types in human leg muscles. Acta physiol. scand. 1975. 93. 135-1 38. Relationship between isometric endurance performance at 50% of maximal voluntary isometric contraction (MVC)and skeletal muscle fibre composition has been elucidated in 19 physical education students. This was found to be linear and the equation corresponded to: y = 9 . 3 5 f 1.093~;r=0.70 (endurance time expressed in seconds and fibre composition as percent slow twitch muscle fibres (ST) of the vastus lateralis muscle). As it is assumed from previous studies that similar isometric tensions preferentially recruit fast twitch muscle fibres (FT) and that the muscle at the point of exhaustion exhibits maximal values for lactate accumulation, it is suggested that lactate formed in F T fibres is released and stored in nonrecruited S T fibres. The ability to sustain similar isometric tension would then be depending on how large the fraction of ST fibres is that can serve as a lactate recipient for lactate producing FT fibres.
Isometric tensions corresponding to 30-50% of maximal leg voluntary isometric contraction (MVC) have been shown to produce maximal values for muscle lactate concentrations a t the point of muscular exhaustion (Karlsson and Ollander 1972, Karlsson et al. 1974). Lower and higher relative tensions, respectively, were demonstrated to cause submaximal phosphagen depletions as well as submaximal lactate accumulations in spite of muscular exhaustion. Repeated exhaustive isometric contractions at tensions corresponding to 30-80% of MVC did not change the metabolic pattern obtained after the first contraction; no further accumulation of lactate did occur (Karlsson er al. 1974). Furthermore, it has been demonstrated that at isometric tensions corresponding to approximately 25 % of MVC or less only slow twitch fibres (ST) were depleted on their glycogen content, as indicated by periodic acid Schiff (PAS) stainings (Gollnick el al. 1974). At tensions in excess of 25% only the fast twitch fibres (FT) were glycogen depleted. The interpretation was, that only FT were recruited to maintain high tensions, whereas at lower tensions only ST were recruited. This conclusion about the recruitment pattern seemed to be in contradiction to results from Molbech et al. (1973), who investigated isometric endurance in muscles with different contractile characteristics and consequently, most likely, with different fibre 135
I36
B. H U L T ~ N ,A. THORSTENSSON, B. SJODIN AND J . KARLSSON
populations. They showed that isometric endurance time at 50% of MVC was longer for muscles with predominantly slow twitch characteristics than for muscles with predominantly fast twitch properties. To further investigate how fibre composition is related to isometric endurance, 19 subjects were examined at a tension corresponding to 50% of MVC, and muscle biopsies were obtained for fibre-typing. It was demonstrated that isometric endurance at this intensity was positively correlated to the percentage of slow twitch fibres.
Methods 19 students of physical education participated in the study. For antropological and physiological data, see Table I. The experiments were performed in an isometric chair, as described by Karlsson and Ollander (1972) by pressing the feet against an immovable bar whereby activating mainly the thigh muscles. MVC was determined on 2 consecutive days and from these data individual tensions corresponding to 50% of MVC were calculated. The endurance tests were performed on the third day. The subjects reported
in the laboratory early in the morning after a light breakfast and the experiments were performed without any preceding maximal tests. Muscle biopsies (Bergstrom 1962) were obtained from vastus lateralis on one of the first two days and analyzed for fibre types according to Gollnick e r a/. (1972).
Results and Discussion Individual MVC ranged 195-400 kp (mean 245 kp) and fibre composition 38-69?/, ST (mean 54% ST) for the experimental group (Table I). No relationship was found between individual MVC and fibre type composition. Endurance time at 50% MVC ranged 56-94 sec and was related to the individual fibre type composition (Fig. I), demonstrating an increased performance with a higher percentage ST fibres. These findings are in accordance with the conclusions of Molbech et af. (1973), that endurance is related to the quality of the muscle with respect to fibre type composition. A previous study suggested that isometric tensions in excess of approximately 25 % of MVC are produced by the recruitment of FT fibres (Gollnick et af. 1974). However, in the present study maximal tensions could not be related to the percentage FT fibres indicating additional factors of significance for peak tension. Since blood flow at tensions corresponding to 50% MVC are severely restricted with n o or very little oxygen delivery to the contracting fibres (for further discussion see Eklund 1974), the anaerobic glycolysis will be utilized for ATP resynthesis (Karlsson 1971). Lactate will then accumulate in the fibres and be released into the extra-cellular fluid and the venous blood. Since venous lactate efflux from contracting muscle already during conditions similar to dynamic exercise has been shown to be limited (Karlsson 1971 and TABLE 1. Mean va1ueskS.E. for age, weight, height, maximal isometric tension (MVC), and percent slow twitch fibres (ST) of the examined muscle (vastus lateralis).
Number of subjects
Age years
Weight kg
Height cm
MVC kp
%, S T
Fibre composition
n - 19
24k0.8
74.2+ 3.1
179+2
245+ 14
54+9
I37
ISOMETRIC ENDURANCE AND MUSCLE FIBRE TYPES
90 t-
100
0 0
80 0
70 -
60-
50-
y 9 45*10'~~X
40 -
r - 070
0
0
304
1
'
40
50 % of slow twitch
60
70
hbers
Fig. 1. Relationship between individual endurance time and percent slow twitch fibres of the examined muscle (vastus lateralis).
Jorfeldt pers. corn.), the rate of lactate accumulation in the contracting muscle during isometric exercise will most probably be much more pronounced as compared to dynamic exercise. The lactate anion in itself has been demonstrated to be a potent inhibitor of lactate formation during in vitro conditions (Karlsson, Hult6n and Sjodin 1974). If this is true also in situ, it seems reasonable to assume a subsequent arrest of the glycolysis at peak values of lactate accumulation due to the fact that the whole extramitochondrial pool of N A D will be transferred into a reduced form (Sund 1968). If so, the release of lactate to other compartments than the venous blood ought to be detrimental for the capability of the muscle to sustain an isometric contraction. Nonrecruited ST fibres is one very probable recipient of released lactate. In addition ST fibres might be able to metabolize lactate formed in FT fibres. The prerequisites for lactate oxidation in skeletal muscle in terms of the heart specific LDH isozymes are present in ST fibres (Karlsson et al. 1974). Moreover, ST fibres have been shown to contain larger amounts of myoglobin than FT fibres (James 1968).
References BERGSTRBM, J . Muscle electrolytes in man. Srand. J. din. Lab. Inrest. 1962. Suppl. 68. EKLUND,B. lnfluence of work duration on the regulation of muscle blood flow. Artu physiol. scand. 1974. Suppl. 411. GOLLNICK, P. D., R. B. ARMSTRONG, C. W. SAUBERT IV, K . PIEHL,B. SALTIN.Enzyme activity and fiber composition in skeletal muscle of untrained and trained men. J. uppl. Physiol. 1972. 33. 312-319. GOLLNICK, P. D., B. SIBDIN,J. KARLSSON, E. JANSSON and B. SALTIN. Human Soleus Muscle: A comparison of fiber composition and enzyme activities with other leg muscles. Pflugers Arch. gus. Physiol. 1974348. 247-255.
138
B.
HULTEN,
A. THORSTENSSON, B. S J ~ D I NAND J. KARLSSON
JAMES,N. T. Histochemical demonstration of myoglobin in skeletal muscle fibres and muscle spindles. Nature (Lond.) 1968. 219. 1174-1 175. KARLSSON, J. Lactate and phosphagen concentrations in working muscle of man. Acru physiol. scand. 1971. Suppl. 358. KARLSSON, J. and B. OLLANDER. Muscle metabolites with exhaustive static exercise of different duration. Arta physiol. scand. 1972. 86. 309-314. KARLSSON, J., B. H U L T ~ Nand B. SIBDIN.Substrate activation and product inhibition of LDH activity in human skeletal muscle. Acta physiol. scand. 1974. 92. 21-26. KARLSSON, J., C. F. FUNDERBURK, B. ESSLNand A. R. LIND.Constituents of human muscle in isometric fatigue. J . appl. Physiol. 1974. In press. MOLBECH, S. and S. H. JOHANSEN. Endurance time in slow and fast contracting muscle groups. Worki~nrironnr.-hlth.1973. 10. 62-64. SUND, H. The pyridine nucleotide coenzymes. In Biological oxidations, ed. T. P . Singer. Interscience Publ. New York. 1968. 603-639.
