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Blood Lactate Response and Critical Speed in Swimmers aged 10-12 years of Different Standards

By B.S. Denadai (1 *); C.C. Greco (1) and

M. Teixeira (2)

(1) Human Performance Laboratory, Department of Physical Education, UNESP, Rio Claro and (2) Department of Physical Education, UNAERP, Ribeirão Preto, Brasil

(*) Address all correspondence to B.S. Denadai, Av. 24, 1515 Bela Vista, Rio Claro, SP, CEP 13506-900, Brasil. Email: Diese E-Mail-Adresse ist vor Spambots geschützt! Zur Anzeige muss JavaScript eingeschaltet sein!

Reproduced from Journal of Sports Sciences, 2000, 18, 779-784

Accepted 21st January 2000

 

It has previously been shown that measurement of the critical speed is a non-invasive method of estimating the blood lactate response during exercise. However, its validity in children has yet to be demonstrated.

The aims of this study were…

1. To verify if the critical speed determined in accordance with the protocol of Wakayoshi et al, is a non-invasive means of estimating the swimming speed equivalent to a blood lactate concentration of 4mmol 1-1 in children aged 10-12 years

2. To establish whether standard of performance has an effect on its determination ... 16 swimmers were divided into two groups – beginners and trained.

 

They initially completed a protocol for determination of speed equivalent to a blood lactate concentration of 4mmol l-1. Later, during training sessions, maximum efforts were swum over distances of 50, 100 and 200m for the calculation of the critical speed. The speeds equivalent to a blood lactate concentration of 4mmol 1-1 (beginners=0.82+ 0.09m·s-1, trained=1.19 + 0.11m·s-1; mean + s) were significantly faster than the critical speeds (beginners = 0.78 + 0.25m·s-1, trained=1.08 + 0.04m·s-1) in both groups.

 

There was a high correlation between speed at a blood lactate concentration of 4mmol 1-1 and the critical speed for the beginners (r=0.96, P<0.001), but not for the trained group (r=0.60, P>0.05). The blood lactate concentration corresponding to the critical speed was 2.7+1.1 and 3.1+0.4mmol 1-1 for the beginners and trained group respectively. The percent difference between speed at a blood lactate concentration of 4mmol 1-1 and the critical speed was not significantly different between the two groups.

At all distances studied, swimming performance was significantly faster in the trained group. Our results suggest that the critical speed underestimates swimming intensity corresponding to a blood lactate concentration of 4mmol 1-1 in children aged 10-12 years and that standard of performance does not affect the determination of the critical speed.

INTRODUCTION

 Blood lactate responses to exercise have been used to evaluate the aerobic capacity of sedentary and active individuals as well as competitive athletes (Weltman 1995). Being a submaximal parameter, the blood lactate response to exercise is more appropriate than maximal oxygen uptake (VO2max) for evaluating the effects of training and, because of its strong correlation with endurance performance, it can be used to prescribe individuals’ intensity of aerobic training (Sjödin et al 1982; Coyle et al 1988).

 The most common term used to describe the blood lactate response during exercise is the anaerobic threshold. This represents the highest intensity of exercise at which a balance between the production and removal of lactate occurs (Heck et al 1985). Methods for the determination of the anaerobic threshold use either a direct or an indirect protocol. With direct protocols, fixed (4mmol 1-1; Heck et al 1985) or variable (Stegmann et al 1981; Tegtbur et al 1993) concentrations of blood lactate are used.

In swimming, the determination of speed corresponding to a blood lactate concentration of 4mmol 1-1, using the concept of critical speed, has been proposed as an indirect means of evaluating this parameter, because it is not always possible or convenient to determine speed at this concentration through analysis of blood lactate (Wakayoshi et al 1992a). This method is both practical and applicable, which permits its use with more athletes.

 

Wakayoshi et al 1992a, defined critical speed as the swimming speed that could theoretically be maintained without exhaustion. The critical speed was expressed as the slope of a straight line between swimming distance at each of six predetermined speeds and duration.

Comparing the critical speeds of well-trained swimmers aged 16-24 years, measured in a swimming-flume and in the swimming pool, using best performances at fixed distances (100, 200 and 400m), Wakayoshi et al 1992b, found a significant correlation between critical speed obtained in the swimming-flume and in the swimming pool (r=0.82, P<0.05), speed at a blood lactate concentration of 4mmol 1-1 and critical speed in the swimming pool (r=0.89, P<0.01) and speed at a blood lactate concentration of 4mmol·1-1 and critical speed in the swimming-flume (r=0.85, P<0.01).

 

Those authors suggested that critical speed could be determined from the relationship between the swimming distance and time recorded, not only in the swimming-flume but also in the swimming pool.

 

However, no study has verified the ability of critical speed to estimate the blood lactate response in children. In swimming, athletes begin intensive training at an early age (9-11 years). Therefore, it is important to confirm the ability of critical speed to estimate the speed at a blood lactate concentration of 4mmol·1-1 in children, who tend to have a lower blood lactate concentration than adults at submaximal and maximal intensities (Eriksson and Saltin 1974), because of lower glycolytic enzymes concentrations and the increased concentration of oxidative enzymes.

As performance in swimming can be determined not only by physiological factors but also by such factors as technical ability and competitive tactics, it is unclear whether this method can be used in the swimming pool with individuals with less technical competence and experience and, consequently, poorer performance, as it can with competitive swimmers.

The aims of this study were…

1. To verify whether critical speed, determined by the protocol proposed by Wakayoshi et al 1992b, can be used as a non-invasive method for the determination of speed at a blood lactate concentration of 4mmol 1-1 in children aged 10-12 years

2. To verify whether standard of performance has an effect on its determination

METHODS

Participants

 

The participants were 16 swimmers aged 10-12 years of age. They formed two groups…
  1. Beginners: 10 swimmers (4 boys, 6 girls) who were concentrating on improving their stroke style, who had 1-2 years of experience of swimming and who had been involved in a training programme four times a week with a weekly median training volume of 8000m. Their physical characteristics were … age=11.2 + 0.9 years, body mass=39.4 + 8.2kg and height=150 + 7cm (mean + s).
  2. Trained: 6 swimmers (3 boys, 3 girls) who were in a training phase, who had 3-5 years experience of swimming and who had been involved in a training program six times a week with a weekly median training volume of 20,000m. Their physical characteristics were … age=11.1 + 0.9 years, body mass=41.1 + 6.4kg and height=152 + 5cm.

 

All the procedures of the study were explained to the children. After obtaining their verbal consent, the children’s parents signed a consent form. The Ethics Committee of Ribeirão Preto University approved the study.

Test Protocol

 

Tests for the determination of speed at a blood lactate concentration of 4mmol 1-1 and critical speed were randomly performed in a 25m pool, with 3-5 days between the two tests. All participants were familiarised with the procedures before testing began.

Determination of Critical Speed

 

During training sessions, the participants were instructed to swim distances of 50, 100 and 200m, using the front crawl stroke, as quickly as possible; they were never instructed to swim at a constant speed. The time taken to swim each distance was recorded. One event was swum per day in random order. Critical speed was determined from the linear regression between swimming distance and the time taken to swim it.

Figure 1 shows determination of critical speed for a member of the trained group in accordance with the method proposed by Wakayoshi et al 1992b. The slope of the line represents the intensity of swimming corresponding to critical speed.

Image50

Figure 1 – Determination of critical speed (CS) for one member of the trained group in accordance with the method of Wakayoshi et al 1992b. Critical speed = 1.07m s-1.

Determination of speed corresponding to a blood lactate concentration of 4mmol·l-1

 

For determination of speed at a blood lactate concentration of 4mmol·1-1, we used the protocol proposed by Mader et al 1976. The participants swam 200m using the front crawl stroke both at 90 and 95% of maximum speed for the distance (as determined previously during the training sessions). A rest of more than 15 minutes was allowed between the two tests.

One and three minutes after each swim, 25m l of blood was collected from an earlobe and placed in microcentrifuge tubes containing 50m l NaF (1%) for measurement of lactate (YSI 2700 STAT). Using linear interpolation, we determined the speed corresponding to a blood lactate concentration of 4mmol 1-1.

Determination of blood lactate concentration corresponding to the critical speed

 

Using the blood lactate concentrations and their respective speeds recorded in the test for the determination of the speed at a blood lactate concentration of 4mmol 1-1, the blood lactate concentration corresponding to critical speed was determined by linear interpolation.

Statistical analysis

 

Comparison between critical speed and the speed at a blood lactate concentration of 4mmol 1-1 within the same group was made using Student’s t-test for dependent variables. The correlation between these speeds was calculated using Pearson’s correlation coefficient.

Student’s t-test for independent data was used to compare the different variables for the beginner and trained groups.

The Mann-Whitney rank sum test was used to compare the percent difference in speed at a blood lactate concentration of 4mmol 1-1 and the critical speed in the two groups. Throughout, the results are presented as the mean + standard deviation. Significance was set at P<0.05.

RESULTS

 

Table 1 presents values for the percent speed attained in a maximal 200m swim and the blood lactate concentrations recorded in the first and second repetitions for the beginner and trained groups during the test to determine speed at a blood lactate concentration of 4mmol 1-1.

For most participants, the determination of speed at a blood lactate concentration of 4mmol 1-1 was based on linear interpolation, not extrapolation, since the blood lactate concentration recorded in the second repetition was above 4mmol 1-1.

Table 1 – Percent speed obtained in a maximal 200m swim (% V200) and blood lactate concentration observed in the first and second repetition for the beginner and trained groups during determination of the speed corresponding to a blood lactate concentration of 4mmol 1-1 (mean + s)

% V200

Lactate (mmol 1-1)

Group

First

Second

First

Second

Beginner

92.2+1.9

96.1+1.9

3.9+0.9

4.7+1.0

Trained

90.5+1.8

94.8+1.7

3.2+0.6

4.1+0.7

Table 2 presents the speeds at a blood lactate concentration of 4mmol 1-1 and the critical speeds for the beginner and trained groups. The speed at a blood lactate concentration of 4mmol 1-1 was significantly faster than the critical speed for the beginners (0.82+0.09 versus 0.78+0.25m·s-1; P<0.001) and for the trained group (1.19+0.11 versus 1.08+0.04m·s-1; P<0.03).

Both speeds were significantly faster (P<0.001) in the trained than in the beginner group. However, the percent difference in the speed at a blood lactate concentration of 4mmol 1-1 and critical speed was not significant (P>0.05) between the two groups.

Blood lactate concentration corresponding to critical speed was not significantly different between the two groups (beginners=2.71 + 1.13mmol 1-1; trained=3.13 + 0.41mmol 1-1;P>0.05).

Table 2. The speed corresponding to a blood lactate concentration of 4mmol 1-1 (V4) and critical speed (CS) for the beginner and trained groups during front crawl swimming (mean + s)

Group

V4

CS

% difference

Beginner

0.82+0.09

0.78+0.25a

7.16+3.01

Trained

1.19+0.11b

1.08+0.04a,b

9.14+6.35

a = P<0.05 in relation to V4 within the same group

b = P<0.05 in relation to beginners

 

Figure 2 and 3 show the relationship between the speed at a blood lactate concentration of 4mmol 1-1 and critical speed for the beginner and trained groups, respectively. There was a high correlation between the two speeds in the beginner group (y=0.11+0.94x, r2=0.92,r=0.96, P<0.001), but not in the trained group (y=-0.60+1.66x,r2=0.36, r=0.60, P>0.05).

 

In the beginner group, the standard error of the estimate (SEE) for the speed at a blood lactate concentration of 4mmol·1-1 was very small, just 3% of the mean speed at a blood lactate concentration of 4mmol 1-1. That in the trained group was somewhat higher, 8% of the mean speed at a blood lactate concentration of 4mmol 1-1.

 

 

Image51

Figure 2 – Relationship between the speed corresponding to a blood lactate concentration of 4mmol 1-1 (V4) and critical speed for the beginners. The dashed line is the line of identity; the solid line is the regression line.

 

Image52

Figure 3 – Relationship between the speed corresponding to a blood lactate concentration of 4mmol·1-1 (V4) and critical speed for the trained group. The dashed line is the line of identity; the solid line is the regression line.

The swims over distances of 50, 100 and 200m for the trained group (1.48+0.04, 1.31+0.02 and 1.21+0.03 m·s-1 respectively) were significantly faster (P<0.001) than those for the beginners (1.28+0.14, 1.07+0.15 and 0.91+0.11m·s1 respectively).

DISCUSSION

 

The main finding of this study was that both the beginner and trained groups recorded mean speeds at a blood lactate concentration of 4mmol 1-1 that were significantly faster than those for critical speed. This is not in agreement with studies performed with adults (Wakayoshi et al 1992b, 1993) under similar exercise conditions.

New studies have applied the concept of critical speed in young swimmers. In swimmers aged 8-18 years, Hill et al 1995, found a strong correlation between critical speed and speed in an endurance swim both in training sessions (183-2286m; 8-10 years: r=0.92; 11-13 years: r=0.99; 14-18 years: r=0.94) and in competition (457-1509m; 11 years: r=0.92; 15 years: r=0.92).

 

Hill et al, proposed that the critical speed is a valid measure to predict aerobic performance in swimming, even in very young swimmers; it does not require blood sampling or other invasive techniques. However, Hill et al, did not compare critical sped with any method for the determination of the speed at a blood lactate concentration of 4mmol 1-1.

Wakayoshi et al 1992a were the first to extend the concept of critical power from a power-time relationship in cycle ergometry to a speed-time relationship in swimming. They found no significant difference (1.16+0.05 versus 1.16+0.03m·s-1) but a high correlation (r=0.94,P<0.01) between critical speed and the speed at a blood lactate concentration of 4mmol 1-1 in a group of well-trained swimmers aged 16-24 years, suggesting that critical speed is a useful indirect parameter for the determination of the blood lactate response and, consequently, aerobic capacity.

 

This is in line with the initial studies of critical power of Monod and Scherrer 1965. Subsequently, Wakayoshi et al 1993, also found a high correlation (r=0.91, P<0.01) between critical speed and the speed at a blood lactate concentration of 4mmol·1-1, suggesting that critical speed might correspond with the exercise intensity at maximal lactate steady state in a group of trained college swimmers aged 18-20 years.

The blood lactate response to exercise in children can explain the difference between the mean values of critical speed and the speed at a blood lactate concentration of 4mmol 1-1 found in the present study. During exercise performed at submaximal intensity, children have lower blood lactate concentrations than adults.

 

The factors responsible for this were addressed by Eriksson and Saltin 1974 and Berget al 1986, in boys aged 6-17 years; they found that, with increasing age, the activity of the glycolytic enzymes tends to increase, whereas the activity of the oxidative enzymes tends to decrease. This suggests that there is a lower ratio of glycolytic to oxidative enzyme activity in children, which could be related to reduced production of lactate, increased oxidation of lactate, or both.

 

The blood lactate concentration at the critical speed in the beginner and trained groups in the present study was 2.7 and 3.1 mmol 1-1 respectively. These values are higher than those reported by Williams and Armstrong 1991, who suggested a fixed value of 2.5mmol 1-1 instead of 4mmol 1-1 as the reference for the determination of maximal lactate steady state in children of this age.

 

However, the results of Williams and Armstrong 1991, should be treated with caution, since higher blood lactate concentrations corresponding to maximal lactate steady state (4-5mmol 1-1) have been reported for children of a similar age (Mocellin et al 1990, 1991; Beneke et al 1996). Moreover, these studies were performed using different exercises protocols (treadmill and cycle ergometer) than the present study (swimming), which might affect the blood lactate concentration corresponding to maximal lactate steady state (Beneke and von Duvillard 1996).

Although we did not determine maximal lactate steady state, the critical speed appears to approach this state or the intensity that could theoretically be maintained without exhaustion during swimming

As the speed at a blood lactate concentration of 4mmol·1-1 was faster than critical speed in the two groups in the present study, and the percent difference between these two speeds was not significantly different, we suggest that standard of performance did not affect the determination of the critical speed.

 

Therefore, that critical speed was lower than the speed at a blood lactate concentration of 4mmol 1-1 was probably the result of the physiological characteristics of the age group studied, since Wakayoshi et al 1993, reported that critical speed measured in a swimming pool can be used to determine the speed at a blood lactate concentration of 4mmol·1-1 in 18-20-year-olds.

In our study, we found no significant correlation between critical speed and the speed at a blood lactate concentration of 4mmol 1-1(r=0.60) in the trained group, whereas there was a significant correlation in the beginners (r=0.96); this suggests that standard of performance can affect the relationship between critical speed and the speed at a blood lactate concentration of 4mmol 1-1 in children aged 10-12 years.

 

However, these results should be treated with caution, since this relationship might have been affected by the small number of participants and the low coefficient of variation for critical speed (3%) in the trained group.

In conclusion, critical speed underestimates the intensity corresponding to speed at a blood lactate concentration of 4mmol 1-1 in swimmers aged 10-12 years.

However, critical speed appears to approach the intensity corresponding to maximal lactate steady state, since the lactate concentrations recorded were close to the values proposed by Williams and Armstrong (1991). Standard of performance does not appear to affect the determination of critical speed, because there was no significant difference in measured parameters between the two groups.

References

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