Acta physiol. scand. 1972. 86. 309-314 From .the Department of Physiology, Gyninastik- och idrottshijgskolan, Stockholm, Sweden

Muscle Metabolites with Exhaustive Static Exercise of Different Duration

BY

JAN KARLSSON and Bo OLLANDER

Received 11 February 1972

Abstract

KARLSSON, J. and B. OLLANDER. Muscle metabolites with exhaustive static exercise of different duration. Acta physiol. scand. 1972. 86. 309-314.

Concentrations of ATP, CP, glycogen and lactate were determined in the lateral portions of the thigh at rest and at different percents (75, 50, 25 and 10 7%) of the individual maximal voluntary isometric contraction (MVC). Endurance times were 0.5, 1.6, 5.8 and 38.7 mm respectively. A phosphagen depletion of 15 mmol x kg-l wet muscle and a lactate accumulation of 20 mmol X kg-1 was obtained only with the 50 96 MVC which is similar to what is observed with short time exhaustive bicycle exercise. At both higher and lower intensities phosphagen depletion and lactate accumulation were less.

Dynamic muscle exercise in man, such as bicycling and running, has been studied extensively with regard to both circulatory and metabolic demands. Static exercise, however, has not been investigated to the same extent. Although various circulatory responses to static muscle contractions have been examined (Humphreys and Lind 1963, Lind et al. 1964, 1966, 1967 and Freyschuss 1970), few metabolic studies appear in the literature (Bergstrom et al. 1970). This is the case in spite of such intriguing characteristics as a high energy turnover without performing any external mechanical work. Moreover, there is, except for very mild tensions, an inadequate oxygen supply due to the occlusive effect on the capillary bed caused by sustained muscle contraction.

The present study was undertaken to evaluate the degree of lactate accumulation and phosphagen depletion in the active muscle groups of man at different per- centages of the maximal static force sustained to exhaustion.

Subjects, Procedure and Methods 3 healthy, male physical education students participated in this study. Some of their characteris- tics are presented in Table I. Static exercise was performed in a chair constructed for leg extension exercise. The angle between femur and tibia was 90". The force generated was measured via a strain gauge located on an immovable iron bar under the subjects' arches.

309

310 TABLE I. Pertinent individual anthropological and physiological data.

Subject Age Weight Height Maximal static force (MVC)

JAN KARLSSON AND DO OLLANDER

years kg cm (kp, 90" extension)

PB 23 75 189 195 SC 22 62 171 205 SJ 21 85 193 161

TABLE 11. Individual data in two subjects for muscle concentration of ATP, C P and lactate before, during and after a sustained static contraction a t 10 % of the MVC (see Table I.). The contraction was interrupted for a few seconds to take the biopsy the same time as the 50 ( I ) and 25 yo (11) tension was terminated due to exhaustion.

Rest I I1 Exhaustion

Subj. ATP CP* Lac- Time ATP CP* Lac- Time ATP CP* Lac- Time ATP CP* Lac- tate* tate* min * tate* min * tate*

SJ 4.7 14 .51 .3 2 . 6 7 4 . 5 16 .62 .1 7 . 9 8 5 . 6 1 1 . 5 2 . 2 36.005.1 1 0 . 5 4 . 1 PB 4.4 12.7 1.3 1.13 4.9 12.0 2.5 5.35 5.4 10.9 4.1 45.004.2 8.3 5.6

* *

* mmoles x kg-1 wet muscle.

The zero level was equal to the tension developed with the legs resting on the bar. The bar- strain gauge assembly was calibrated with adequate weights prior to the experiments. Maximal voluntary contraction (MVC) for each subject was determined repeatedly in preliminary ex- periments a few days prior to the studies. The final experiments were performed until ex- haustion at 75, 50, 25 and 10 % of the MCV on separate days. I n additional experiments 2 of the subjects were studied while maintaining the lowest force for times corresponding to those attained at 50 and 25 % of the MVC (see Table 11). The experiments were conducted over a 3 week period.

Biopsies for the determination of muscle metabolites were taken from the lateral parts of the quadriceps femoris muscle before (in supine position) and after (within 3-5 s ) the exercise with the subject still sitting in the chair. The specimens were immediately frozen in liquid nitrogen and stored at -70" until analyzed for glycogen, lactate, ATP and C P as described earlier (Karlsson 1971). Blood samples were simultaneously taken from a prewarmed hand (fingertip blood) and analyzed for lactate concentration according to Scholz ef a/,. (1959).

Results The pattern of niaxirnal endurance time and relative force was similar to that reported by Monod and Scherrer (1957) and later by Rohmert (1960). Thus, maximal endurance time increased rapidly when the relative force was less than 20-25 "/c (Fig. 1 ) . Phosphagen depletion (ATP and CP) was more pronounced with the 50 and 25 % tensions. This was primarily produced by CP depletion with only a small reduction in ATP stores (Fig. 2 ) . This is in contrast to what is observed during bicycle exercise, where a CP depletion to about 2 mmolx kg wet muscle (as the case with the 50 "/o tension) is acompanied by a significant ATP depletion (Karlsson, Diamant and Saltin 1970, Karlsson 1971).

MUSCLE METABOLITES IN EXERCISE 31 1

f E l-

Y

9

z C U 3

W

Fig. 1. Maximal endurance time for static muscular contraction in relation to percent of maximal static force (MVC) . % OF MAXIMAL FORCE'

The pattern of muscle lactate concentration with isometric exercise was similar to that of CP depletion (Fig. 2 ) . The highest average concentration ( 2 1.8 mmol x kg wet muscle) was found with the 50 'j% tension exhaustion time. Lactate con- centration of the thigh was lower in all 3 subjects both at higher (75 "/.; 0.5 min duration) and lower ( 2 5 %; 5 .8 min duration) relative tensions (average value 10.3, 14.0 and 4.0 mmol x kg

Blood lactate concentrations immediately at the end of the exercise did not exceed 6-7 mmolx 1 (Fig. 2 ) and were 2-3 time lower than in the muscle at all inten- sities. Blood lactate concentrations were similar at rest and at the lowest load of tension. Even though blood lactate concentrations were low they changed in a pattern similar to that of muscle lactate. At tensions corresponding to 10 % MVC main- tained for times that produced exhaustion at 50 and 25 c/o of MVC a gradual de- crease in CP concentration and increase in muscle lactate concentration occurred (Table 11) .

wet muscle with 75, 50, 25 and 10 yoo, respectvely, of the individual maximal static force. However, a considerable variation existed both intra- and interindividually. The inconsistent picture for glycogen depletion may be attributed to the fact that the methodological error is larger for the glycogen than the lactate determination (Karls- son 1971). One glucose residue produces 2 molecules of lactate, during anaerobic glycolysis which will enhance the uncertainty when relating lactate formation to glycogen depletion.

wet muscle with 75, 25 and 10 7'0 respectively of MVC).

The glycogen depletion averaged 27, 25, 33 and 16 mniol glucose unitsxkg

312 JAN KARLSSON AND BO OLLANDER

6 r ATP 1

- ifi Muscle lactate

f Rest . 75

00 50 25

w

of MVC

0 dynamic exercise - a a static - * - - - - - u ,

5 10 15 20 25 30 i I

MUSCLE LACTATE, m moles x kg-' wet muscle

Fig. 2 Fig. 3

Fig. 2. Mean values and range for ATP, CP, muscle and blood lactate concentrations at rest and at exhaustion in the different experiments with different percents of MVC (see Fig. 1 ) . Fig. 3. The relation between simultaneously obtained muscle and blood lactate concentrations for static and dynamic exercise. I n the figure are included the present mean values ( o ) , data from one subject (a, a) studied at different dynamic and static exercise loads to exhaustion (unpublished results) and data from Karlsson and Saltin (1970) (a).

Discussion

From the phosphagen depletion and the lactate concentration data it could be con- cluded that the largest anaerobic output occurred when 50 "/o of the MVC was sustained for 1.6 min. With this tension the phosphagen depletion and lactate con- centration in the contracting muscle was similar to maximal values obtained during short-term maximal bicycle work (Karlsson and Saltin 1970, Karlsson 1971). At the other test tensions lower values were obtained for the phosphagen depletion and lactate concentration in the muscle.

In a recent study by Bergstrom at al. (1971) muscle metabolism was examined in relation to isometric exercise but with a somewhat different type of leg extension contraction. Bergstrom et al. found that the ATP depletion at the two tensions studied, maximal and 40 "/o of MVC respectively, were small compared to what usually was observed with dynamic exercise in relation to a corresponding decrease for CP concentration. Moreover, they demonstrated a more pronounced CP deple- tion and lactate accumulation with the 40 % tension compared to the maximal.

No values were obtained concerning the aerobic energy output during the static

MUSCLE METABOLITES IN EXERCISE 313

exercise. The oxygen delivery to the contracting muscle is depending on the magni- tude of the blood flow and to what extent it is nutritive. Barcroft and Miller (1939) reported that in the calf muscle the blood flow might be occluded at isometric con- tractions corresponding to more than 20 "/o of MVC, thus with higher tensions limiting the aerobic energy output to the amount of molecular oxygen present in the muscle at the start of contraction. Humphreys and Lind (1963) have modified this concept by demonstrating an increased blood flow compared to resting levels in the forearm at as high tensions as 60 % of MVC, but with a very pronounced post- exercise hyperaemia (Lind et aZ. 1964) indicating that the existing blood flow was far from adequate. A restricted blood supply might affect the muscle tissue in many respects, e.g. as already emphasized an inadequate oxygen delivery, a diminished outflow of anaerobic metabolites and a reduced conductance of heat away from the contracting muscle. The steeper concentration gradient between blood lactate and muscle lactate after static compared to dynamic exercise supports the suggestion of a restricted blood flow through the muscle during static contractions.

Both heat accumulation and lactate concentration have been suggested as being closely related to the experience of muscular fatigue during bicycle exercise of 2---20 min duration (Karlsson 1971). Akre and Aukland (1970) have studied the heat generation in human forearm muscle during maintained as well as rhythmic isometric contractions and found it to be related to relative tension, but according to their findings the calculated muscle temperature increase in the present study might only be 1-2' C which is less than found during exhaustive bicycle exercise of 2--20 min duration (Saltin et al. 1972). The role of temperature as a main limiting factor might then be excluded of these reasons.

The low blood lactate versus the high muscle lactate concentrations might indicate a higher yradient between muscle and blood for static as compared to dynamic exer- cise (Fig. 3). The most reasonable explanation for this seems to be the occlusive effect on the capillary bed with sustained static tensions causing a delayed efflux as already discussed above.

Another indication that an aerobic energy yield was absent or very small when pushing with 50 and 75 % MVC is that in these 2 expts. the product of tensionx time is very similar and much less than in the experiments with 10 and 20 "/o of MVC. I t may be worth mentioning that according to Hoes et al. (1968) only up to 15 % of MVC is used during maximal bicycle work which can be sustained for 4-6 min.

It has been mentioned that the highest anaerobic energy output in terms of phosphagen depletion and lactate iormation was found with the 50 $% tensions. The reason why lower muscle lactate concentrations and phosphagen depletions were obtained with the other tensions cannot fully be explained at present. Different re- cruitment patterns of muscle fibers with different contraction tensions might limit the phosphagen depletion and the lactate accumulation to only the fibers recruited. Local factors within these fibers would then limit the performance of all the muscle. The values for phosphagen depletion and lactate accumulation obtained in a biopsy

314 J A N K A R L S S O N A N D BO OLLANDER

specimen represent a number of fibers. Differences in ATP, CP, as well as lactate concentration within the analyzed specimen might then be expected. However, ad- di tional factors cannot be excluded as of importance to the experience of muscular fatigue at those tensions where maximal phosphagen depletions and lactate accumu- lations were not observed.

This study was supported by grants from Swedish Medical Research Council (project 4OX-22031 and the Research Council of the Swedish Sport Federation.

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