Acta Physiol Scand 1981, 1 1 1 : 465-469

Lactate concentrations after short, maximal exercise at various glycogen levels

IRA JACOBS

Laboratory for Human Performance, Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden

JACOBS, 1.: Lactate concentrations after short, maximal exercise at various glycogen levels. Acta Physiol Scand 1981. 111:465469. Received 23 July 1980. ISSN 0001-6772. Laboratory for Human Performance, Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden.

The present study was designed to evaluate the effects of changes in glycogen concentra- tions on lactate accumulation in human skeletal muscle during a 1 min maximal muscle fatigue test (MFT). All subjects first performed the MFT duringa control experiment. Four subjects then performed the MFT again 1 h after prolonged exercise. Seven other subjects performed the MFT again after a 3 day carbohydrate (CHO) poor diet and again after 4 additional days of a CHO rich diet. The rn. vastus lateralis was biopsied prior to (for glycogen determinations) and immediately after (for lactate determinations) each perfor- mance of the MFT. High but similar lactate concentrations were observed (22.3 mmol X

kg-I w.w.) with normal and supernormal glycogen leves. Lactate was significantly reduced following both the prolonged exercise (to 7.0 mmol x kg-’ w.w.) and the CHO poor diet (to 16.8 mmol x kg-’ w.w.). Alterations in muscle strength and fatigue patterns were also observed after the dietary manipulations but they were neither commensurate with the changes in metabolite concentrations nor statistically significant.

K e y words; Glycogenolysis, lactate, muscle fibre type, strength, muscle fatigue, diet

Muscle glycogen depletion has been related to changes in the capacity for endurance exercise per- formance (for ref. see Costill & Miller 1980), but the effect of glycogen levels on parameters of short time, maximal performance requiring energy to be produced by predominantly “anaerobic” pathways has not been extensively examined. Concomitantly with the severe glycogen depletion observed after prolonged exercise at an intensity of 65%-85% VO,max, several investigators have found that sub- sequent exhaustive exercise results in a diminished capacity to raise blood lactate concentrations (Sal- tin & Hermansen 1%7, Karlsson 1971, Asmussen et al. 1974). Karlsson (1971 a) found that when maxi- mal exercise was performed after prolonged work, muscle lactates were similar but blood lactates de- creased when compared to the control expt. One factor common to the findings described above is the decrease in glycogen concentration induced by the prolonged exercise. Newsholme & Crabtree (1979) have postulated that “a decrease in substrate concentration at a reaction which is not saturated with substrate, but which initiates the pathway,

would reduce the flux through that reaction and the pathway”. Thus, the reduced blood lactates ob- served following prolonged exercise may be the result of an impaired flux through glycogenolysis and anaerobic glycolysis. To further clarify this possibility the present study was designed to examine the relationship between resting muscle glycogen concentrations and the intramuscular lac- tate accumulation following a short (-1 min), maximal muscle fatigue test (MFT). A wide range of resting glycogen concentrations was induced by either previous prolonged exercise or a combination of exercise and dietary manipulations.

METHODS Two series of experiments were carried out. In series I changes in resting glycogen concentrations were achieved by previous standardized exercise consisting of both sub- maximal (-75 % V02max) and supramaximal, “sprint type” activities. This has been described in detail elsewhere (Jacobs, Kaiser & Tesch 1980). In series 11, subjects underwent the classical glycogen loading prog- ramme (Bergstrorn et al. 1967). They depleted glycogen

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466 1. Jacobs

stores in the m. vastus lateralis by cycling at approximate- l y 70% of their previously extimated VOlmax (via heart rate nomogramme according to Astrand & Rodahl, 1971) for 90 min. followed by alternating bouts of cycling at 150% V0,max for 1 min and resting for 3 min, until voluntary exhaustion. These subjects then adhered to a diet composed of primarily fat and protein (-70% of total energy intake) for 3 days after which they were restricted to a carbohydrate (CHOI rich diet (-80% total energy intake) for 4 days.

In both series of expts. all subjects performed the MFT in the normal state after reporting to the laboratory for the first time. The second session occurred after experimental manipulation of intramuscular glycogen concentrations. Thus. in series I the MFT was performed prior to the standardized exercise programme and again I h after its completion. In series 11, the MFT was performed in the normal state. again after the 3 days of the fat and protein diet. and once more after the 4 days of the CHO rich diet.

'4 detailed description of the MFT has been presented earlier (Thorstensson 1976, Tesch 1980). Briefly. the sub- jects were required to perform 50 consecutive. maximal extensions at the knee while sitting in a chair with the lower leg attached to the lever arm of a Cybex I F (Lumex, New York) isokinetic dynamometer. Angular velocity was set and maintained at 180" x s-'. Both peak torque. i.e. the torque produced during the strongest con- traction. and torque decline. expressed as the absolute difference in Newton-meters between peak torque and the average of the last 3 contractions. were recorded.

Immediately prior to each performance of the MFT a muscle biopsy was obtained from the m. vastus lateralis using the percutaneous needle biopsy technique (Bergstrom 1962). This sample was divided into 2 por- tions, one of which was mounted in embedding medium frozen in isopentane cooled with liquid nitrogen, and stored for later histochemical analysis. The other portion was immediately frozen in liquid nitrogen and stored at -80°C for biochemical quantitative determination of glycogen concentration. Within 3-5 s following comple- tion of the MFT another muscle biopsy was obtained from the same incision, frozen in liquid nitrogen and stored at -80°C for the later determination of lactate concentration. Muscle fibres were classified as type I (slow twitch, ST) or type I1 (fast twitch, FT) after staining for myofibrillar ATPase activity (Padykuia & Herman 1955) following preincubation at pH 10.3 and 4.3 (Brooke & Kaiser 1970). The average number of fibers counted to calculate fiber type distribution was 463 (range: 225-674). Muscle metabolites were analysed using samples which were weighed at -20°C. freeze dried and reweighed. The calcu- lated change in weight due to water content was then used to express all metabolite concentrations per wet weight. Samples were dissected free of blood and connective tis- sue under a dissection microscope prior to assay. Glycogen content was determined after acid hydrolysis as glucose residues using an enzymatic fluorometric technique (Lowry & Passonneau 1973). Lactate concent- ration was determined using an enzymatic fluorometric technique as described by Karlsson (1971).

Mean values (range) for pertinent descriptive data relat- ing to all subjects in both series of experiments are as

follows: age-23.4 (19-34) years, height-iig (170-185) cm, weight-70.9 (56-82) kg, muscle fibre composition- 56.9 (4069) percent fast twitch. 4 subjects psrticipated in series I and 7 in series 11. All were sedentary males.

Results in series I were subjected to the S:udent's r-test for paired observations in order to test the significance of differences. A one-way analysis of variance IANOVA) for repeated measures was applied to the data from series 11. Subprogramme P2V from the Biomedical Computer Prog- rams package (Dixon & Brown 1977) was used. When the ANOVA indicated significance between trials, the Dun- can Multiple Range Test was applied to determine its location (Klugh 1970).

RESULTS

Intramuscular concentrations of glycogen were sig- nificantly altered by the exercise and dietary proce- dures (Fig. I ) . Glycogen concentrations were similar in the normal condition for both series of experi- ments and were therefore combined and expressed as one mean "control" value for both series. This control value was 96.2k3.74 (S.E.) mmoles glucoayl units x kg-' wet muscle. The lowest con- centrations were exhibited in series 1, one hour following the standardized laboratory exercise programme (36.7k8.0). In series 11, the exercise combined with 3 days of a fat and protein rich diet resulted in higher glycogen concentrations than those in series I (O. lS>P>O. 10) yet 5 2 % lower than the control values after a normal mixed diet (P<O.OS) . The additional 4 days of a CHO rich diet in series I1 resulted in a two fold increase in in- tramuscular glycogen content when compared to normal, control values (P<O.OS).

Muscle lactate concentrations were similar (P>O.OS) when the MFT was performed after the mixed diet and after the CHO rich diet. Following the fat rich diet in series 11, muscle lactate after the MFT was significantly lower (P<0.005) than in the normal and the glycogen loaded conditions (Fig. I ) . Lactate accumulation in series I was significantly lower than that after the fat and protein rich diet in series I1 ( P < O . O O S ) .

In order to illustrate the relationship between substrate availability and end product accumula- tion. pre-MFT muscle glycogen concentrations were plotted against post-MFT lactate concentra- tions (Fig. 2 ) . Supernormal glycogen concentrations neither facilitated nor inhibited lactate production when compared to normal glycogen concentrations. However, once a glycogen concentration of ap- proximately 40 mmol x kg-' W.W. was attained the

Ac /,I Phr.sio( Scand I I I

Lactate, glycogen und short, maximal exerciw 467

I

150 I Glycogen concentration, glucosyl units. mmolcs I kg-’ w. w. 100

501 Loctate concentration, mmoles x kg-’ W.W.

20 -

15 -

10 -

h Series I ( n 4

I 1 DISCUSSION

AllSs Series1 Seriesa (n=ll (n.4) (n.7)

Fig. 1 . Mean values and S.E. are shown for glycogen levels prior to performance of the muscle fatigue test, and lactate levels in muscles sampled immediately after the test. Abbreviations refer to the control expt. (C); series 1 after the glycogen depletion standardized exercise (Ex); series I1 after the fat and protein rich (F+P) and the carbohydrate rich (CHO) diets.

subsequent lactate production was significantly re- duced following the MFT.

The experimental procedures also resulted in changes in the variables associated with perfor- mance of the MFT. Peak torque produced following the CHO rich diet and the fat diet was slightly reduced when compared to the control situation (Fig. 3) yet not statistically significant ( f 5 0 . 2 5 ) . The same pattern was observed regarding torque decline during the 50 contractions. Force loss was slightly lower following both the fat rich (O.IO>P>0.05) and CHO rich diets (P>0.25) as compared to the normal situation. Significant de- creases in both peak torque and torque decline fol- lowing the prolonged exercise in series I were also observed and reported elsewhere (Jacobs, Kaiser & Tesch 1980).

The major finding in the present study is that mus- cle lactate levels are significantly decreased, as compared to a control experiment, when the MFT was performed 1 h after preceding prolonged exer- cise. This phenomenon was also evident when the MFT was performed after maintaining low glycogen concentrations during 3-4 days of a fat rich (CHO poor) diet.

Depleted glycogen stores after prolonged exercise have been previously implicated as responsible for the reduced blood lactate accumulation found upon subsequent short duration, maximal intensity exer- cise (Saltin & Hermansen 1967). The present find- ings suggest that a similar relationship may exist intracellularly . These findings may possibly reflect increased lactate utilization during exercise and not necessarily a decreased production. However, the short duration of the MFT probably does not suffice to allow this possibility to account for the dramati- cally decreased lactate concentrations. Since re- duced lactate concentrations were observed follow- ing both the exercise and diet manipulations, the suggestion that the lack of substrate at a flux generating reaction (glycogen : phosphorylase) will in turn reduce flux through the entire metabolic

‘

pathway stimulated seems to be applicable to the present findings (Newsholme & Crabtree 1979).

The severe changes in glycogen content induced by the experimental procedures must be accom- panied by commensurate changes in the water con- tent ofthe muscle cell, due to the approximately 3 4 g of water bound to each g of glycogen (Olson & Saltin 1970). With the weighing and freeze drying techniques used in this study, we have accounted for differences in intracellular water content when expressing metabolite concentrations. One ought to consider the intracellular response to lactate ac- cumulation in the hydrated as opposed to the rela- tively “dehydrated” muscle cell as a function of the changes in glycogen content. However, a search of the literature failed to reveal a study examining the effects of dehydration on intramuscular lactate ac- cumulation during exercise of a duration and inten- sity similar to that employed in the present study.

The changes in resting glycogen concentrations caused by both the exercise and dietary manipula- tions follow the same patterns reported by others (Bergstrom et al. 1967). It is doubtful that these changes could directly affect phosphorylase, there- by accounting for the reduced lactate accumulation.

Acra Physiol Scand 111

468 I. Jacobs

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* * * *

- 0 . 0 * * 8' 20 -

* c post aerclse Lactate concentratim. mmlls xkg-' w w -

3

125 H Mixed

Fat-rich CHO-rch I;:::::- 50 75

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151

i\mounts of phosphorylase far in excess of that required for high rates of glycogenolysis are nor- mally present in muscle (Gollnick et al. 1978). How- ever, a few days of energy intake consisting predo- minantly of fat and protein has been shown to result in increased resting muscle citrate and glucose-6- phosphate (G-6-P) levels when compared to a sirni- lar duration of predominantly carbohydrate intake (Jansson 1980, Klausen & Sjagaard 1980). Thus, the model of glycolytic inhibition being mediated via and/or parallel to increased intramuscular citrate and G-6-P (Newsholrne & Start 1979) may be applicable to series 11. Changes in respiratory ex- change (R) values indicate a reduced relative energy

following a fat rich diet (Christensen & Hansen 1939, Bergstrom et al. 1967, Jansson 1980). This was also the case when exercise intensity was "supermaximal" with a duration of 2 min (Klausen & Sjegaard 1980). Significant intramuscular lipid utilization during maximal exercise performance of a duration shorter than the MFT performed in the present study has been previously demonstrated (Essen, Hagenfeldt & Kaijser 1977).

The concentration of intramuscular citrate is greater following prolonged exercise than at rest (Essen, Hagenfeldt & Wahren 1977, Jansson 1980). Thus a concomitant inhibition of glycolysis may contribute directly to the reduced lactate concentra-

yield from carbohydrates and an increased fat oxi- dation both at rest and during submaximal exercise Intense exercise probably stimulates phos-

tions in both series of experiments.

Torque, Nm

Fig. 3. Torque produced during the 50 repeated contractions of the muscle fatigue test after the different dietary manipulations in series 11.

Lactate, glycogen and short, maximal exercise 469

phorylase to such an extent that its saturation with glycogen may determine the rate of glycogenolysis. Thus, Klausen & Sjergaard (1980) offer further em- pirical support for the Newsholme & Crabtre mo- del (1979) of low glycogen concentrations them- selves limiting glycogenolytic rate due to insuffi- cient utilization of potential enzymatic activity.

In summary, when a muscle fatigue test was per- formed with normal and supernormal glycogen con- centrations in the activated musculature, high but similar lactate concentrations were observed fol- lowing exercise. When glycogen levels were sig- nificantly decreased by either prolonged exercise or a combination of exercise and dietary manipula- tions, lactate levels following performance of the fatigue test were significantly reduced. Alterations in muscle strength and fatigue patterns were also observed as a function of the dietary changes. However these alterations were not nearly as ex- tensive as the observed metabolic changes within the muscle. The energy requirement to cover the demand of the 50 contractions of the MFT has been estimated for active males and previously reported (Nilsson, Tesch & Thorstensson 1977). The relative contribution of the various energy substrates to such exercise has not been investigated nor is it within the scope of the present study. Possible changes in substrate utilization, implicated by the reduced exercise lactate levels in the glycogen de- pleted state, must be the subject of further study.

The author gratefully acknowledges Dr Jan Karlsson for his constructive criticism of the manuscript and his help with the biopsy procedures, and Rikard SchCle for statisti- cal advice. This study was supported in part by the Coca- Cola Export Corporation, Sweden.

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