Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man

Acta Physiol Scand 1982, 114: 461-466

Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man

IRA JACOBS and PETER KAISER

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

JACOBS, I . & KAISER, P.: Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man. Acta Physiol Scand 1982, 114:461-466. Received 28 Aug. 1981. ISSN 0001-6772. Laboratory for Human Performance, Department of Clinical Physiology, Karolinska Hospital, Stockholm, Sweden.

The relationship between muscle and blood lactate levels during progressively step-wise incrementing cycle exercise has been investigated in 10 male subjects. Steps between power outputs during exercise were SO W and each stage, from loadless pedalling until voluntary exhaustion, lasted 4 min. Blood samples and biopsies (m. vastus lateralis) were taken for lactate determination at each power output beginning with the exercise intensity perceived by the subject as being “rather moderate”. The ratio muscle: blood lactate was greater than one at all power outputs and increased most markedly at the power output closest to that eliciting 4 mmol x I - ’ blood lactate (W,,,,,,). At WOHI..4. blood lactate was positively correlated to muscle lactate concentrations which covaried widely among subjects (mean 8.3. range 4.5-14.4 mmol x kg-l wet weight). Muscle fibres from the W,,,,., biopsy in 6 subjects were dissected out and identified as fast twitch (FT) or slow twitch (ST). No significant difference in lactate concentration was observed between pools of FT or ST fibres.

K r y ic~wd.~: Blood and muscle lactate, submaximal exercise, fast twitch and slow twitch muscle fibres

Attempts have been made to construct models for the prediction of muscle lactate levels from blood conccntrations measured during submaximal exercise typically conceived of as representing a metabolic “steady state” (e.g. Freund & Zouloumain 1981). However, great inter-subject variation and differences observed in the relationship of muscle to blood lactate levels during exercise of varying intensities, question the validity of interpreting blood lactate as being representative of muscle lactate concentration (Bergstrom et al. 1971, Karlsson 1971, Knuttgen & Saltin 1972, Jorfeldt et al. 1978).

Blood lactate during submaximal exercise has been demonstrated to be reflective of muscle metabolic characteristics (Jacobs 1981). The exercise intensity corresponding to a blood lactate concentration of 4 mmol x I - ’ is correlated to the percentage of slow twitch muscle fibres in the active muscles (Sjodin &Jacobs 1981), to capillary density and frequency (Sjodin & Jacobs 1981, Tesch et al.

1981) and to the ratio between glycogenolytic and Krebs cycle ”marker” enzyme activities (Sjodin et al. 1981). In addition, the exercise intensity at which blood lactate begins to increase during submaximal exercise is a strong predictor of endurance running performance (Farrell et al. 1979, Sjodin & Jacobs 1981, Lafontaine et al. 1981).

Most studies which report muscle and blood lactate levels have either utilized a discontinuous exercise protocol or examined only one or two submaximal exercise intensities in addition to maximal exercise. This causes difficulties when at- tempting to relate the results to the continuous, step-wise incremental protocol used for the determination of onset of blood lactate accumulation (OBLA) (Jacobs 1981). Thus one purpose of the present study was to examine the relationship between muscle and blood lactate during cycle exercise using a continuous step-wise protocol. Of particular interest was the muscle to blood lactate

Acra Physiol Sumd 114

so w Mean SD Range n 100 w Mean SD Range

I5OW Mean SD Range n 200 w Mean SD Range n

250 w Mean SD Range n

300 W Mean SD Range n

350 w Mean SD Range n

n

I .2 0.6 0.3-2 .0

10

I .7 0.7 0.3-2.4

10

2.5 0.7 1.1-3.6

10

3.3 1.3 I .7-5.3

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5.8 2.6 3.1-1 1.2

10

8.6 2.0 5.2- 10.5 8

8.5 - -

I

I .x - - I

2.9 0.9 1.9-3.8 4

4.2 2.7 1.4-8.6 8

7.5 3.3 4.5- 14.4 8

14.6 8.3

9

17.5 4.5

10.4-22.5 7

18.5

6.9-28. I

- -

I

I .06 - - I

I .4x 0.47 I .06-2.06 4

I .58 0.72 0.74-2.97 x

2.65 I .28 1.44-5.35 8

2.49 I .22 1.065. I I 9

2. I 6 0.66 1.25-3.23 7

2.18 - -

1

99 22

10

I I5 18

90-141 10

140 20

114-168 1 0

161 19

129-186 10

177 16

148-200 10

I 88 13

165-205 8

202

67-128

- - I

51 10 3663 10

60 7

4X-69 10

73 7

62-80 10

84 6

74-93 10

93 5

85-100 10

99 2

94- 100 8

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24 4

19-31 I 0

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38-6 I 10

70 12 57-92 10

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gradient at an exercise intensity close to that which elicits 4 mmol x I - ' blood lactate (W,,,,,.,).

A method has been previously described for the determination of metabolite concentrations in fragments of individual muscle fibres and in pools of either fast twitch or slow twitch fibres dissected out and identified from one and the same skeletal muscle biopsy sample (Essen et al. 1975). With this method it has been demonstrated that there is a greater accumulation of lactate within the fast twitch than in the slow twitch muscle fibres when high intensity (> 100% Vo2 max) exercise, leading to exhaustion within 30 s-3 min is performed (Essen & Hgggrnark 1975, Tesch 1980). N o data are availa- ble regarding lactate accumulation in the main fibre

types during submaximal exercise in humans. Thus. an additional purpose of the present study was to determine the concentration of lactate in pools of either fast twitch or slow twitch muscle fibres from biopsies obtained at an exercise intensity close to WI,,,,., .

METHODS Sithjrc/.s. 10 males accustomed to heavy exercise partici- pated as subjects after being informed o f the protocol and a l l associated risks. Their mean (range) age. weight and height were22.9(18-33)yrs, 73.4(65-85)kg, 180(174-190) cm.

Prorotwl. A biopsy was obtained at rest from the m . vastus lateralis using the percutaneous needle technique

Table 2. Merrrr ~ d r r r s , SD rrrid rtrtigr fbr wri trhles tnrrrsrrred (11 tiir e.wrci.sp itrtensity p ~ r / i ) r t i i i d c h c ~ s t to t l i irt cwlcirlated to elicit 4 riirnol x I-‘ blood Iirctirte in 9 iiirrlr sithjrcts

Muscle Blood lactate

Power level lactate (mmol x kg-l, Musclelblood HR HR Wl,Il,.., (w) (mmol x I - ’ ) w .w. ) lactate (b x min-0 (lo max) (9%)

Mean 206 3.5 x.3 2.33 163 84 94 SD 39 0.4 3.1 0.62 20 9 4 Range 150-250 3.0-4. I 4.5- 14.4 I .50-3.51 I11180 62-93 Xb107

(Bergstrom 1962) and two other incisions were prepared in each leg to enable rapid biopsies during exercise. Sub- jects mounted an electrically braked (Siemens-Elema) cycle ergometer and performed loadless pedalling for 4 min. Thereafter, the power output was increased by 50 W every 4 min until the required pedalling frequency (60 rpm) could not be maintained. When a subject could not complete 4 min, the previous power output was considered as maximal. During the final 45 s at each stage the following procedures were carried out: heart rate was recorded via an ECG; finger tip blood (25 p l ) was sampled for blood lactate determination (Strom 1949); the subject ceased pedalling, placed his leg on the handlebars while being supported from behind, and a biopsy was obtained from one of the previously prepared incisions (left and right legs alternated). The biopsy pro- cedure required approximately 10 s from the time the subject ceased pedalling until the needle containing the muscle sample was frozen directly in liquid nitrogen. The first exercise biopsy was taken when the subject rated the exercise as equal to or greater than “2” on a 10 point perceived exertion scale developed by Borg (1981). The semantic description corresponding to this rating was “rather moderate”. Biopsies were then taken at the end of each subsequent exercise intensity. Based on the relationship between the various exercise intensities and blood lactate concentration, the intensity corresponding to 4 mmol x I - ’ blood lactate was calculated (Jacobs 1981) and will be referred to as the power output at onset of blood lactate accumulation (Wl,,l.A).

His tochemicd and biochemical methods. The resting muscle sample was frozen in isopentane cooled with liquid nitrogen. Serial sections were stained for ATPase (Padykula & Herman 1955) after preincubation at a pH of 10.3 (Brooke & Kaiser 1970). Fibres were subsequently classified as slow twitch (type I , ST) or fast twitch (type 11, FT). Mean fibre area and the relative area occupied by each fibre type were calculated on NADH stained fibres (Novikoff et al. 1961) with a cutting and weighing method described previously (Thorstensson 1976. Tesch 1980).

Exercise biopsy specimens were stored at -80°C until analysed. They were freeze-dried and fibre fragments were dissected out from the sample under a light micros- cope. Lactate concentration was determined in triplicate using fluorometric, enzymatic methods (Lowry & Pas- sonneau 1972) described in detail by Tesch (1980). In addition, in 6 subjects the biopsy sample from the exercise intensity closest to the calculated W,,,,, was further

analysed. A small fragment of each dissected-out fibre (75-100 fibres) was stained for ATPase and identified as either FT or ST (Essen et al. 1975). Pools of either FT or ST fibres were then separately analysed (in triplicate) for lactate concentration as described above. All lactate concentrations are expressed per kg wet muscle weight with water content assumed to be 77% of muscle weight (Karlsson 1971).

RESULTS

The mean values for the variables measured have been tabulated for all power outputs beginning with SOW (Table I ) . In Table 1 . each exercise intensity is also expressed relative to the calculated W,,,,,,,, (% W,,,,,.,). In this manner the power output performed which was closest to the calculated W,,,,,,,\ for each subject could be identified and the parameters averaged (Table 2 ) . One subject’s data are not included in Table 2 since the biopsy sample obtained at the

E 4.0 $ 4 U

m - ” z 3.5

r = 0.89, p<O.OOl 1 / y = 2.52 * 0 . 1 2 x

3 . 0 5 &A I I I

-~ 4 8 12 16 Muscle lactate, mmol x kg-l W.W.

Fig. 1 . The relationship of blood lactate to muscle lactate concentrations at an exercise intensity close to that which elicits 4 mmol x I - ’ blood lactate.

Actu Physiol S c a d 114

Table 3. Dri t l r , fbr 6 .sitbjccisjiotn thr poLtvr I P L ~ c h ) s r s t t o W,,lil,,, 'The mixed fibres lactate concentration was calculated with the following formula (Tesch 1980): (FT lactate x %FT area) + (ST lactate x %ST area)

Muscle lactate

Power Blood Mixed ST FT 7% level H R HRmax lactate fibres Fibres Fibres FT/sT

Subject FT area (W) ( h x min-I) (b x min-) (mmol x I - , ) (mmol x kg-', wet weight) lactate

AD 70.4 I50 I60

AL 58.2 250 I73 51.2 200 180 62.4 200 177

AW 43.6 250 I73 Mean 60.3 217 I75 SD 12.0 40.8 9.3

M A 75.9 250 188

;g 200 3.6 6 .8 9.7 5.6 0.58 202 5.3 15.6 13.7 16.2 1.18 I85 7.0 6 .3 5 .6 6.8 1.22 205 3.0 4.6 4.1 5 .1 I .24 190 4. I 14.4 16.3 13.3 0.82 I92 4.0 11 .3 9.3 13.9 I .50 196 4.5 9.8 9.8 10.2 I .09

7.8 1.4 4 .6 4.6 4.9 0.33

power output closest to W,,l,l,,, could not be used for lactate determination.

The calculated W,,,,, *, averaged (SD) 219 (36) W for the 10 subjects and values ranged from 163 to 263 W. Muscle and blood lactate levels increased exponentially with exercise intersity. Mean concentrations at the power output closest to W,,,,l.,A and at exhaustion were 8.3 and 20.1 mmol x kg-I respectively in muscle; blood lactate concentrations were 3.5 and 8.9 mmol x I - ' . The muscle/blood lactate ratio increased most markedly, suggesting a steeper musclelblood gradient, first at 200 W which was the performed power output closest to the calculated mean W,ll,l.,\ (i.e. at 94% W,,,,.,).

When the power output closest to W,lHl.., for each subject was examined, muscle and blood lactate levels were correlated (Fig. I ) (r=0.89, p<O.OOI). No significant correlation was evident between blood or muscle lactate levels respectively and either absolute or relative heart rate at the power wtput closest to W,,,,,:,. Neither absolute nor relative heart rate were related to any single exercise intensity expressed as 5% W,IH,.A. However, when data from all exercise intensities were plotted to- gether, absolute heart rate was correlated to % W,,,,,, (r=O.77, p < O . O I ) as was relative heart rate ( I = 0.90, p < 0 .OO I ).

No significant difference was observed between the lactate concentrations of pools of FT and ST fibres in the biopsies examined from the power output closest to the calculated WOHLA (Table 3). Four of the 6 subjects demonstrated slightly higher lactate levels in the FT fibres while two subjects had higher levels in the ST fibres. These differences

were not related to muscle fibre type composition nor was the lactate concentration in mixed, FT or ST fibres related to muscle fibre type at this exercise intensity.

DISCUSSION

The present study describes the relationship between muscle and blood lactate levels during submaximal cycle exercise using a continuous, step- wise incremental protocol. The gradient for lactate concentration between the muscle and blood compartments varied greatly among subjects at all intensities including that closest to W,,Hl.,4, however the mean absolute values for blood and muscle concentrations are similar to those reported earlier (e.g. Karlsson et al. 1970, Knuttgen & Saltin 1972, Saltin et al. 1974. Lollgen et al. 1981). Since OBLA has been shown to be related to skeletal muscle metabolic characteristics (Jacobs 1981 1, of particular interest was the lactate gradient between muscle and blood at an exercise intensity approximating W,,,i,-,,. Tesch et al. (1982) have also recently examined the gradient between muscle and blood lactate although their subjects exercised precisely at the predetermined W,,,i,,,4 when the muscle and blood samples were obtained. The muscle/blood lactate ratio at W,,HI.A was identical to that observed in the present study (i.e. 2.3) where the mean exercise intensity was 94% of the calculated WIIHI. ..\.

A major finding in the present study was the strong positive relationship between blood and muscle lactate at the exercise intensity closest to WOHI.A in spite of the small range in blood lactate

Musch/hlood Incttrte with siihmtl.rimrrl exercise 465

values (i.e. 3.0-4.1 mmol x 1 - l ) which did not leave much room for covariation between the variables. This correlation was not evident at exercise intensities corresponding to 50, 75, or 125% WORI.A, and the correlation coefficients between muscle and blood lactate were r = 0.18, -0.21 and 0.04 respectively. Thus, our data suggest that within the limita- tions of the protocol used, blood lactate does reflect muscle lactate at exercise intensities close to 100% W,,RI,A. This is in contrast to Tesch et al. (1982) who found no correlation between blood and muscle lactate when exercise was performed at the predetermined W,)BI.A. The experimental protocols may explain the different findings. The steps between power outputs were 50 W in the present study. The protocol employed by Tesch et al. involved 30 W steps while the last step to the predetermined WoRI.A varied between subjects from 10-30 W (P. Tesch, personal communication). I t is possible that these differences may have affected the rate of equilibra- tion between the muscle and blood compartments.

During steady state exercise lactate release in- creases linearly with exercise intensity until muscle lactate levels of about 5 mmol x kg-' wet weight are attained at which point the rate of release plateaus (Saltin et al. 1974, Jorfeldt et al. 1978). On this basis, we must assume that lactate release is maximalized at exercise intensities which approxi- mate OBLA since the mean muscle lactate concentration at WOBl.A in the present study is in excess of the plateau threshold described above. This sup- position is further supported by the narrow range in blood lactate values at WOBLA, in spite of the large differences in muscle lactate, suggesting that lactate release at this exercise intensity is probably not related to muscle lactate concentration. In contracting, in situ dog muscle Graham et al. (1976) also reported no correlation between lactate release and muscle lactate levels at relatively low concentrations.

The percentage of slow twitch fibres has been shown to be related to OBLA during treadmill running (Sjodin & Jacobs 1981) and during cycle exercise (Tesch et al. 1981). This is in part due to the enzymatic profile of the ST fibre which favours oxidative combustion and is less favourable to anaerobic glycogenolysis leading to the production of lactate, than that of the FT fibre (Essen et al. 1975, Sjodin 1976). In addition, a greater capillariza- tion is associated with the ST fibres, and capillary density is related to OBLA during running and cy-

30-825873

cling (Sjodin & Jacobs 1981, Tesch et al. 1981). A tendency towards covariation between the absolute WOBI.A and percent S T fibres in the vastus lateralis was also found in the present material (r=0.55 , p = O . 10). Muscle fibre composition was not related to absolute muscle lactate values, the FT/ST fibre lactate gradient, nor the muscle to blood ratio in the present study. Graham (1978) has previously reported that the muscle to blood lactate ratio is in- versely related to the percentage of ST fibres in the exercising muscle, although it is puzzling that Lollgen et al. (1981) describe a positive relationship between the same variables when referring to the same or a similar study.

With increasing exercise intensity it has been demonstrated that initially ST fibres and then progressively more FT fibres are recruited (Gollnick et al. 1974). The glycogenolytic profile of the FT fibre suggests that it may produce more lactate at submaximal exercise loads than the ST fibre, as has been demonstrated for supramaximal exercise (Es- sen & Haggmark 1975, Tesch 1980). Moreover, fast glycolytic muscle is the only fibre type which accumulates lactate levels in excess of the blood concentration in exercising rats (Baldwin et al. 1977). However, one must keep in mind that the different rat muscles examined by Baldwin et al. (1977) are homogeneous in their fibre type while human leg musculature is mixed. Therefore, the present findings regarding lactate content of pooled FT and ST fibres should be considered as descrip- tive in nature and should not be interpreted as im- plying that there is no difference between fibre types in lactate production during submaximal steady state exercise. The 4 min duration between the onset of the exercise intensity close to OBLA and the biopsy would allow for sufficient time for diffusion of lactate from muscle to blood, from one muscle fibre to another, or the oxidation of lactate as fuel by the contracting fibres. These confounding factors suggest that the methodology employed is unsuitable for the detection of gradients in lactate production between fibre types during this kind of exercise.

In conclusion, the observed muscle : blood lactate ratio suggested that gradients exist for lactate between muscle and blood during submaximal exercise of a continuous incremental nature which are noticeable already at relatively low intensities. The muscle : blood lactate ratio increased most markedly at an exercise intensity close to that

Acra Physiol Scnnd 114

466 Irir Jtrcdx irrid P . Kcriser

which was calculated to correspond to 4 mmol x I - ' blood lactate. At this exercise intensity blood lactate levels were directly related to muscle lactate levels.

The authors are grateful to Angela Smith M.D., Kerstin Elwin and Gurlith Petersson Stfil for technical assistance. This study was supported by grants from ICI-Pharma, the Swedish Medical Research Council (No. 4251). and Swedish National Defense Research Institute grants (No. .570-.(056:2 01 G-5 I97:4).

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Lactate in blood, mixed skeletal muscle, and FT or ST fibres during cycle exercise in man

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