Cross-country skiing and postexercise heart-rate recovery

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc.

Note. This article will be published in a forthcoming issue of the International Journal of Sports Physiology and Performance. The article appears here in its accepted, peer-reviewed form, as it was provided by the submitting author. It has not been copyedited, proofread, or formatted by the publisher. Section: Original Investigation Article Title: Cross-Country Skiing and Post-Exercise Heart Rate Recovery Authors: Laurent Mourot1,2, Nicolas Fabre3, Erik Andersson3, Sarah Willis3, Martin Buchheit4, and Hans-Christer Holmberg3,5 Affiliations: 1EA 4660 Culture Sport Health Society and Exercise Performance, Health, Innovation Platform, University of Franche-Comté, Besançon, France. 2Clinical Investigation Centre in Technologic Innovation, INSERM CIT808, University Hospital of Besançon, France. 3Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden UniversityÖstersund, Sweden. 4Physiology Unit, Football Performance and Science Department, ASPIRE Academy for Sports Excellence, Doha, Qatar. 5Swedish Olympic Committee, Stockholm, Sweden. Journal: International Journal of Sports Physiology and Performance Acceptance Date: April 6, 2014 ©2014 Human Kinetics, Inc. DOI: http://dx.doi.org/10.1123/ijspp.2013-0445

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc.

Cross-country skiing and post-exercise heart rate recovery Submission Type: Original Investigation

L. Mourot1,2, N. Fabre3, E. Andersson3, S. Willis3, M. Buchheit4, Hans-Christer Holmberg3,5

1 EA 4660 Culture Sport Health Society and Exercise Performance, Health, Innovation platform, University of Franche-Comté, Besançon, France. 2 Clinical Investigation Centre in Technologic Innovation, INSERM CIT808, University Hospital of Besançon, France. 3 Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, 831 25 Östersund, Sweden. 4 Physiology Unit, Football Performance and Science Department, ASPIRE Academy for Sports Excellence, Doha, Qatar 5 Swedish Olympic Committee, Stockholm, Sweden Address for correspondence MOUROT Laurent 19 rue A Paré Bâtiment Socrate - Plateforme EPSI F-25030 Besançon Cedex FRANCE Telephone: +33 3. 63 08 23 23 e-mail: [email protected] Running Head: HRR and cross-country skiing performance Abstract word count: 250 Text-only word count: 3071 Number of Tables: 3 Number of Figure: 1 Disclosures: nothing to disclose

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Abstract

Post-exercise heart rate (HR) recovery (HRR) indices have been associated with running and

cycling endurance exercise performance. The present study was designed 1) to test whether

such a relationship also exists in the case of cross-country skiing (XCS) and 2) to determine

whether the magnitude of any such relationship is related to the intensity of exercise prior to

obtaining HRR indices. Ten elite male cross-country skiers [mean ± SD, 28.2 ± 5.4 years,

181 ± 8 cm, 77.9 ± 9.4 kg, 69.5 ± 4.3 mL⋅min-1⋅kg-1 maximal oxygen uptake ( 2

.OV max)]

performed two sessions of roller-skiing on a treadmill: 1) a 2 x 3-km time-trial and 2) the

same 6-km at an imposed sub-maximal speed followed by a final 800-m time-trial. 2

.OV and

HR were monitored continuously, while HRR and blood lactate (BLa) were assessed during

2-min immediately following each 6-km and the 800-m time-trial. The 6-km time-trial time

was largely negatively correlated with 2

.OV max and BLa. On the contrary, there was no

clear correlation between the 800-m time-trial time and 2

.OV , HR or BLa. In addition, in no

case was any clear correlation between any of the HRR indices and performance time or

2

.OV max observed. These findings confirm that XCS performance is largely correlated with

2

.OV max and the ability to tolerate high levels of blood lactate; however, post-exercise HRR

showed no clear association with performance. The homogeneity of the group of athletes

involved and the contribution of the arms and upper body to the exercise preceding

determination of HRR may explain this absence of a relationship.

Keywords: post-exercise reactivation; time-trial; performance; maximal oxygen uptake;

blood lactate.

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Introduction

Male cross-country skiing (XCS) competitions involve distances from 1-50 km

(covered in about 2-150 min) and performance is highly dependent on whole- and upper-

body aerobic and anaerobic power.1,2 The new racing formats, such as the sprint and the

“Tour de ski”, make even greater demands on skiing rapidly and maintaining high velocities,

as well as accelerating and reaching a high peak velocity at the finish.

Post-exercise heart rate recovery (HRR) is the rate at which the heart rate (HR)

decreases after exercise.3 HRR can be quantified by different indices that have been shown to

be largely to very largely associated with endurance performance, with lower relationship in

cross sectional than longitudinal studies. Endurance training is generally associated with both

faster HRR and improved physical performance, and changes in both variables are largely

related in runners4 and well-trained cyclists.5 In addition, HRR is largely associated with the

running performance of the exercise used to derive HRR 4,6 and the HRR of elite soccer

players following maximal exercise is moderately more rapid than that of less well-trained

players.7

Under any technical and environmental circumstances, these previous investigations

suggest that the best skiers during a cross-country ski race will exhibit the fastest HRR , but

to our knowledge this hypothesis has never been tested. Accordingly, our primary aim here

was to examine relationships between XCS performance and HRR during two time-trials

performed at racing speed. A secondary aim was to evaluate whether the extent of any such

relationship is related to the intensity of the exercise (submaximal versus maximal) that

precedes the determination of HRR.

Methods

Participants. Ten elite male cross-country skiers gave written consent to participate

in the study, which was pre-approved by the Regional Ethical Review Board in Umeå,

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Sweden. They all competed at Swedish national level (senior competition) and have previous

experience of roller-skiing on a treadmill for performance testing and training. Their mean ±

SD age was 28.2 ± 5.4 years, height: 181 ± 8 cm, body mass: 77.9 ± 9.4 kg; maximal oxygen

uptake ( 2

.OV max): 69.5 ± 4.3 mL⋅min-1⋅kg-1 and peak HR: 190 ± 5 bpm, measured during a

roller-skiing test on a treadmill. They were asked to refrain from ingesting caffeine or alcohol

for at least 24 hours before testing, eat a light meal 3 hours before testing, and refrain from

exhaustive training before and between testing sessions.

The experimental protocol. Using the free (skating) technique, all of the athletes

performed three test sessions on a motor-driven treadmill designed for roller-skiing (2.5 m x

3.5 m, Rodby, Södertalje, Sweden). Each participant used the same pair of roller-skis (Pro-

Ski S2, Sterners, Nyhammar, Sweden), which were pre-warmed in a heating box prior to each

test to eliminate any effect of frictional heating on the wheels and bearings. The athletes used

their own ski poles with special pole tips. During all tests, they wore a safety harness secured

to the ceiling.9

The first test session used an incremental protocol to determine maximal aerobic

values, starting at an incline of 4° with a progression of 1° each minute.9 The speed was set to

11 km.h-1; if participants were able to continue beyond an incline of 11°, speed was increased

by 0.3 km.h-1 every 30 s. The three highest values measured with a sampling duration of 10 s

were averaged to calculate 2

.OV max and peak heart rate (HR).

At least 7 days and no more than 1 month after the incremental test, the skiers

performed two test sessions within a 7-day period. The first trial involved roller-skiing for 6-

km (two 3-km loops) as fast as possible (Figure 1). The incline of the treadmill was

programmed in such a manner as to force the skiers to utilize gears 2, 3, and 4 of the skating

technique10 and they were not allowed to change gear on the same segment (Figure 1). The

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. use of these specific gears was imposed according to the slope and skiers were not allowed to

change gear on the same track segment. Two laser beams detected the position of the skier

and adjusted the speed of the belt, if the skier moved to the front (i.e., increasing speed) or

rear (i.e., decreasing speed) of the belt, whilst maintaining skiing speed on the mid-part of the

treadmill. This course configuration reproduced the constraints imposed by a real XCS

race.2,11,12

The second test involved the same two 3-km loops, but performed at 95% of the speed

recorded during the first time-trial and followed by an 800-m time-trial using gear 3 (Figure

1). The aim of this submaximal exercise was to examine whether the magnitude of the

possible association between HRR and performance is affected by the intensity of the

exercise used to derive HRR, with an exercise intensity that is still challenging and could be

achieved during XCS race.

Prior to each time trial, the athletes warmed up for 20-25 min at fixed speeds of 8.5,

10.5 and 15.5 km.h-1, corresponding to approximately 70% of the predicted speed on inclines

1, 2 and 3, respectively, followed by four 6 s sprints during the last 5 min period in order to

prepare the athletes for the forthcoming tests at high roller skiing speeds.

Methodology. Expired O2 and CO2, breathing frequency, tidal volume and the

inspired minute ventilation were monitored continuously during testing with the mixed

expired procedure employing an ergo-spirometry system (AMIS 2001 model C, Innovision

A/S, Odense, Denmark) equipped with an inspiratory flowmeter.9 The gas analysers were

calibrated with a mixture of 16.0% O2 and 4.0% CO2 (Air Liquide, Kungsängen, Sweden)

and calibration of the flowmeter was performed at low, medium and high flow rates with a 3-

L air syringe (Hans Rudolph, Kansas City, MO, USA). Ambient conditions were monitored

with an external apparatus (Vaisala PTU 200, Vaisala Oy, Helsinki, Finland). An electrode

transmitter belt (T61, Polar Electro, Kempele, Finland) holding a Polar S810 HR monitor

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. (Polar Electro, Kempele, Finland) was fitted to the chest of each athlete as instructed by the

manufacturer to continuously record beat-by-beat HR during exercise and subsequent

recovery.14,15,16

Capillary blood (20 µL) was drawn from a fingertip immediately after the completion

of each 36-km trial and of the 800-m time-trial and immediately mixed with a lysing and

stabilizing agent in a safe-lock vial. The concentration of lactate in this blood (BLa) was

determined using a Biosen C-Line Sport Analyser (EKF Diagnostics, Magdeburg, Germany),

calibrated with a standard solution of lactate (12 mmol.L-1) prior to each analysis.9

Heart rate data processing

All data recorded by the S810 were downloaded onto a computer (Polar Precision

Performance SW 4.03, Polar Electro Oy, Kempele, Finland). Occasional irregularity in the

form of extra or skipped heartbeats (i.e., an extra systole and subsequent compensatory

pause) was identified by eye and replaced manually by interpolated values for adjacent

intervals.17

HRR indices. At the end of the two 6-km and 800-m trials, each athlete sat down

immediately (i.e., within 5 s) on a chair on the treadmill to allow the beat-by-beat HR during

the 2-min recovery periods to be analysed. The sitting posture was imposed since body

posture influences HRR13. Three HRR indices were calculated: the first was the absolute

difference between the average HR observed during the first 5 s of monitoring at the end of

exercise and the average HR recorded during the interval 60 s later (HRR60s).14,16 The

second index compensated for possible changes in the HR at the end of exercise by

expressing HRR as a percentage of this value (nHRR60s).18 In addition, a third index was

obtained using semi-logarithmic regression.3 The natural logarithm of the number of times

that the heart beat during the interval 10-40 s after exercise was plotted against the length of

the period of exercise and linear regression analysis then applied. The time constant for the

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. short-term post-exercise decay in HR (T30) could thus be obtained as the negative reciprocal

of the slope of this regression line.

Statistical analyses

Data are presented as mean ± standard deviation (SD) values or mean and 90%

confidence limits (CL) when specified. The Gaussian distribution of the data was verified by

the Kolmogorov–Smirnov goodness-of-fit test (Z value <1.0). When data were skewed or

heteroscedastic, they were transformed by taking the natural logarithm. Since the magnitude

of an effect is of more practical interest than statistical significance per se,19 all comparisons

were also expressed as standardized mean differences (Cohen effect size, ES), calculated

using the pooled standard deviations for the two testing sessions being compared. Threshold

of >0.2 for small, >0.5 for moderate and >0.8 for large ES were used.

Relationships between HR derived indices and performance were established using a

Pearson’s product–moment correlation. The following criteria were adopted to interpret the

magnitude of the correlation (r) between test measures: <0.1, trivial; 0.1–0.3, small; 0.3–0.5,

moderate; 0.5–0.7, large; 0.7–0.9, very large; and 0.9–1.0, almost perfect.19 Also, 90% CL for

the correlations were calculated using a spread-sheet designed for this purpose and

downloaded from http://www.sportsci.org. If the 90% CL overlapped small positive and

negative values, the magnitude were deemed unclear; otherwise that magnitude was deemed

to be the observed magnitude.19

Results

Trial times, cardiopulmonary variables and blood levels of lactate.

The trial times, cardiopulmonary variables and blood levels of lactate during the

maximal and sub-maximal 6-km time-trials and the final 800-m time–trial are presented in

Table 1. During the submaximal 6-km run, the mean 2

.OV over the entire distance was 95.7

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. ± 6.3% of the corresponding values for the 6-km time-trial at maximal speed. The mean HR

was 96.6 ± 2.1% and the BLa at the end was 59.7 ± 10.7% of the corresponding values for

the maximal time-trial, respectively.

The time required to complete the 6-km time-trial at maximal speed was largely

correlated with 2

.OV max, the mean 2

.OV and BLa and very largely with the mean

percentage of 2

.OV max maintained during the overall exercise (Table 2). In contrast, there

was no clear correlations between the time of the 800-m trial and 2

.OV , HR or BLa (all

r<0.51; Table 2).

The HRR indices. HRR values at the end of the maximal and sub-maximal 6-km time-

trials and the final 800-m time–trial are presented in Table 1. T30 was moderately and

positively correlated with performance time on the 800-m time-trial (Table 3). No other clear

correlations between the other indices and trial times were detected (all r <0.39).

Relationships between cardiopulmonary variables, blood levels of lactate and the HRR

indices (Table 3).

In the case of both the maximal and submaximal time-trials, there was no clear

correlation between HRR60s, nHRR60s and 2

.OV max (all r < 0.31). T30 after the

submaximal exercise and the 800-m time trial was moderately and negatively correlated with

VO2max.

Discussion

The major findings of the present investigation were that 1) trial time was not clearly

related to HRR indices, irrespective of the exercise intensity used to derive the indices, 2) the

time required to complete 6-km of roller-skiing on a treadmill at maximal speed

demonstrated a very large negative correlation to the skier’sVO2 max and post-exercise blood

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. levels of lactate, and 3) there was no clear correlation between the different HRR indices and

VO2max.

Many external factors influence the performance of a cross-country skier, including

snow, temperature, ski wax, the skis selected, or possible equipment failure. To eliminate

such influences, we chose to have our subjects perform a standardised time-trial with roller-

skis on a treadmill. All of our skiers had significant previous experience of this type of

performance testing and training.

Both the 6-km time-trial at maximal speed (which took about 20 min) and the same

distance at submaximal speed followed by a 800-m time-trial resemble typical XCS

races.20,21,22 Indeed, the 2

.OV during the trials (>90% of 2

.OV max in all cases) and the post-

race blood level of lactate (~11 mmol.L-1) were similar to the values observed during a

simulated race on snow (84% of 2

.OV max and 9.1 ± 0.8 mmol.L-1).21 Moreover, a traditional

XCS race performed at average exercise involves a 2

.OV close to 90% of 2

.OV max, with a

considerable anaerobic contribution.2,20,21 Altogether, these considerations indicate that the

findings of the current study are relevant to what occurs during actual XCS races. .

The time required to complete the 6-km time trial at race speed demonstrated a very

large and negative correlation to 2

.OV max and, to a lesser extent, the blood level of

lactate.1,23 In contrast, no such relationships were observed in the case of the 800-m time-

trial.2 This difference could be due to the fact that during short events, the discriminating

factor for performance is the coordination of the general strength and power capacities within

the different and complex skiing movements instead of these capacities per se,12 which was

not what was being assessed here.

It is nevertheless important to emphasize that the blood lactate level at the end of an

exercise is just the result of the accumulation of lactate over the whole exercise, and not a

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. precise evaluation of anaerobic energy contribution. Unfortunately, such a precise evaluation

could not be done with the data of the present study. Thus, the impact of the anaerobic

glycolysis is unclear and cannot be excluded for both the 6-km and the 800-m time trials.

The HRR is employed to adjust training and monitor performance.4,18 Endurance

athletes with a high level of performance generally exhibit a rapid HRR,6,7,24 and alterations

in the HRR in response to aerobic training correlate with improvements in performance. 4,5

Such observations formed the basis for our hypothesis that XCS performance would be

related to HRR indices, but no such relationship was apparent here, in agreement with the

similar HRR indices reported after a maximal test among athletes with different endurance

capacities.25

This lack of any relationship may be due to the fact that there is a pronounced genetic

influence on variations in the HRR,26 which might have obscured possible differences related

to fitness. It is also noteworthy that high level skiers were involved in the present study. In

such context, differences in performance might rely more on technical considerations than on

physiological capacities. Indeed, our skiers exhibited coefficients of variation for 2

.OV max

of 6.1% and for the 6-km trial time of 8.4%, which are lower than in other studies (<12%).5,4

Such homogeneity makes it more difficult to identify relationships between variables.

This lack of relationships could also be explained by the intensity of the exercise

preceding determination of the HRR indices. When exercise involves a large anaerobic

energy contribution and blood acidosis is high, greater autonomic perturbations occur as a

result of activation of the metabo/chemoreflex.16 Such activation may make it more difficult

to relate the state of the autonomic nervous system (ANS) to performance employing HRR

indices. Even during the submaximal trial, the lactate value at the end of exercise is high (7.0

mmol/L), which may explain why only two clear relationships between any of the HRR

indices and skiing performance were observed (Table 3). As already mentioned, the impact of

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. the anaerobic contribution is unclear in the present study, but with truly submaximal exercise

(i.e., under the first ventilatory threshold), such relationships might be more apparent.4,18

The mode of exercise utilized here might provide yet another explanation for the lack

of relationships. XCS with the free (or skating) technique involves the entire body, with a

significant contribution by the arms and upper body,1 whereas exercise involving

predominantly the lower body (running or cycling) has been examined in previous studies of

this same nature. 4,5,6,7,24 The HRR has been reported to be more rapid following upper-body

than lower-body exercise, even with the same HR immediately after exercise.27 This

observation indicates more pronounced parasympathetic reactivation after arm exercises, but

no explanation for this is yet available.

To our knowledge, no comparisons of the HRR following XCS and other modes of

exercise have been reported. In addition, there appear to be no studies focusing on the HRR

after exercise that relies predominantly on upper-body performance. Involvement of the

upper-body to different extents, but with similar HR could lead to different relationships

between the HRR and performance for different individuals, a possibility that may explain

our present findings and deserves further investigation.

In the present study, no significant relationship between HRR and the parameters that

show the degree of exhaustion (% 2

.OV max, %HRmax, BLa) were observed. This result

suggested that the interrelationship between HRR and time-trial performance is not

dependent of the degree of exhaustion.

The relationship between HRR indices and 2

.OV max remains unclear, being reported

as non-existent5,14 or moderate-to-large.25,28 Here, the relationship between HRR and 2

.OV

max was inconsistent and dependent on the index employed. Both HRR60s and T30 are

thought to reflect post-exercise reactivation of the vagus nerve 3,16 and thereby the same

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. feature of the ANS, although HRR60s may be more reliable.29,30 The relationship between

T30 and the time required to complete the 800-m trial was actually positive, although a

negative relationship had been expected (i.e., the faster time, the longer T30). Thus, certain of

the relationships found here (e.g., T30 versus performance time and 2

.OV max) should be

taken with caution, since type I error may have occurred with our somewhat limited number

of participants.

Practical considerations

The relationships between HRR indices and XCS performance during a 6-km time-

trial at maximal speed or during a 6-km at submaximal speed followed by a 800-m time-trial

were inconsistent. More precisely, these correlations were of low magnitude and partly in an

unexpected direction (e.g., T30 was positively related to performance time during the 800-m

time trial). Also, no relationship was observed between HRR indices and 2

.OV max. These

results suggest therefore that absolute HRR values may be of limited usefulness for the

diagnostic of XCS performance between skiers. Relative changes in the HRR induced by

training,4,5 rather than differences between athletes, might be of more practical interest.

On the contrary, large correlations between XCS performance and the skier’s 2

.OV

max were observed during the 6-km time-trial, but nor during the 800-km time-trial. This

confirmed that 2

.OV max is a valid tool for the diagnostic of XCS performance in highly

trained skiers during race of about 20 min.

Conclusions

In the present study, trial time was not clearly related to HRR indices, irrespective of

the exercise intensity used to derive the indices. This indicated that, contrary to other sports

involving mainly the lower body (running, cycling or soccer), XCS performance is not

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. associated to HRR. Further investigations are required to establish the contribution of

exercise by the arms and upper body to the HRR and may provide an explanation for the

absence of relationships to performance observed here.

On the contrary, large correlations between XCS performance and the skier’s 2

.OV

max and post-trial blood level of lactate were observed. These associations were not present

in the case of the 800-m time-trial. This indicated that XCS performance largely depends of

2

.OV max and that the anaerobic energy contribution seems of importance, but this should be

confirmed with appropriate evaluation. Over shorter distances (such as 800-m) other non-

metabolic factors (i.e., the neuromuscular system) might exert a more pronounced influence.

Acknowledgements

The authors would like to thank the athletes and trainers involved in this study for their

participation, enthusiasm, and cooperation. This study was supported financially by the

Swedish National Centre for Research in Sports and the Swedish Olympic Committee.

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“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc.

Figure 1. Profiles of the 6-km time-trial at maximal speed (upper) and of the submaximal 6-km time-trial followed by the final 800 m time-trial (lower). HRR = heart rate recovery. G2, G3 and G4 = gear 2, 3 and 4 using the free (skating) cross-country ski technique

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Table 1. Trial times, oxygen consumption (V;

.O2), heart rate (HR), blood levels of lactate

(BLa) and indices of heart rate recovery associated with the 6-km time-trial, the submaximal exercise and the final 800-m time-trial

6-km

time trial Submaximal

exercise 800-m

time trial

Time (min:sec) 20:40 ± 01:43 23:13 ± 03:02 02:07 ± 00:11

2

.OV (mL.min-1.kg-1) 59.1 ± 5.1 56.9 ± 6.7 62.1 ± 5.9

% 2

.OV

max 89.6 ± 4.6 86.3 ± 8.1 94.4 ± 8.2

HR (bpm) 179 ± 7 174 ± 7 189 ± 5

%HRmax 94.4 ± 2.3 91.5 ± 3.5 99.2 ± 2.7

BLa (mmol.L-1) 10.6 ± 1.4 7.0 ± 1.2 10.5 ± 0.8

HRR60s (bpm) 32.6 ± 11.7 27.0 ± 12.5 25.5 ± 9.9

nHRR60s (bpm) 17.7 ± 6.4 15.0 ± 6.9 13.6 ± 5.3

T30 (bpm) 16.0 ± 12.0 14.9 ± 11.9 17.3 ± 10.2

HRR60s = difference between heart rate (HR) at the end of exercise and 60 s later. nHRR60s = HRR60s data expressed as a percentage of the final HR.

T30 = time constant for the short-term (10-40 sec) post-exercise recovery of HR.

n=10

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Table 2. Correlation coefficients (90% confidence limits; 90%CL) between oxygen

consumption ( 2

.OV ), heart rate (HR) and the blood level of lactate (BLa) and time required

to complete the 6-km and 800-m time-trials.

6-km time-trial time 800-m time-trial time

r (90% CL) r (90% CL)

2

.OV max -0.65 (-0.89; -0.16) -0.24 (-0.70; 0.36)

2

.OV -0.59 (-0.86; -0.06) -0.05 (-0.59; 0.52)

% 2

.OV max -0.84 (-0.95; -0.54) -0.34 (-0.75; 0.27)

HR 0.09 (-0.49; 0.61) 0.28 (-0.32; 0.72) %HRmax 0.47 (-0.11; 0.81) 0.51 (-0.06; 0.83)

BLa -0.63 (-0.88; -0.12) 0.18 (-0.41; 0.67)

n=10. In bold are the clear relationships.

“Cross-Country Skiing and Post-Exercise Heart Rate Recovery” by Mourot L et al. International Journal of Sports Physiology and Performance © 2014 Human Kinetics, Inc. Table 3. Correlation coefficients (90% confidence limits; 90%CL) between the final performance time, cardiopulmonary variables, blood levels of lactate and the post-exercise heart rate recovery indexes calculated during the 6-km and 800-m time-trials.

6-km time trial

Final Time 2

.OV max Mean % 2

.OV max Mean % peakHR Final BLa

r 90% CI r 90% CI r 90% CI r 90% CI r 90% CI

6-km Time trial

HRR60s 0.39 (-0.21; 0.78) -0.21 (-0.68; 0.39) -0.21 (-0.68; 0.39) 0.03 (-0.53; 0.57) -0.38 (-0.22; 0.77) nHRR60s 0.37 (-0.23; 0.77) -0.23 (-0.69; 0.37) -0.20 (-0.68; 0.40) -0.04 (-0.58; 0.52) -0.38 (-0.22; 0.77)

T30 0.27 (-0.33; 0.72) -0.13 (-0.64; 0.45) -0.44 (-0.80; 0.15) 0.20 (-0.40; 0.68) 0.47 (-0.11; 0.81)

Submaximal exercise

HRR60s 0.09 (-0.49; 0.61) -0.31 (-0.74; 0.29) 0.07 (-0.50; 0.60) -0.15 (-0.65; 0.44) -0.44 (-0.80; 0.15) nHRR60s 0.07 (-0.50; 0.60) -0.31 (-0.74; 0.29) 0.08 (-0.49; 0.61) -0.17 (-0.66; 0.42) -0.44 (-0.80; 0.15)

T30 -0.36 (-0.24; 0.76) -0.58 (-0.86; -0.04) 0.08 (-0.49; 0.61) 0.25 (-0.35; 0.70) 0.30 (-0.30; 0.73) 800-m time trial

Final Time 2

.OV max Mean % 2

.OV max Mean % peakHR BLa

800-m Time trial

HRR60s -0.21 (-0.68; 0.39) 0.16 (-0.43; 0.65) 0.17 (-0.42; 0.66) -0.27 (-0.72; 0.33) -0.43 (-0.79; 0.16) nHRR60s 0.07 (-0.50; 0.60) 0.15 (-0.44; 0.65) 0.17 (-0.42; 0.66) -0.28 (-0.72; 0.32) -0.45 (-0.80 to 0.14)

T30 0.59 (0.06; 0.86) -0.68 (-0.90; -0.20) -0.50 (-0.82; 0.07) 0.16 (-0.43; 0.65) -0.19 (-0.67; 0.4)

n=10. In bold are the clear relationships.

2

.OV max, = maximal oxygen consumption, HR = heart rate, BLa = blood lactate during the TT.