Glenn Björklund

Biomechanically Influenced Differences in O2 Extraction in Diagonal Skiing: Arm versus Leg

PURPOSE This study aimed to determine whether the differences in oxygen extraction and lactate concentration in arms and legs during cross-country skiing are related to muscle activation or force production and how these differences are influenced by a reduction in exercise intensity. METHODS Nine well-trained male cross-country skiers (age = 22 +/- 3 yr, V˙O2max = 5.3 +/- 0.3 L min(-1) and 69 +/- 3 mL kg(-1) min(-1)) performed diagonal skiing on a treadmill for 3 min at 90% followed by 6 min at 70% of V˙O2max. During the final minute of each workload, arterial, femoral, and subclavian venous blood was collected for determination of blood gases, pH, and lactate. EMG was recorded from six upper- and lower-body muscles, and leg and pole forces were measured. Cardiorespiratory variables were monitored continuously. RESULTS Oxygen extraction in the legs was higher than that in the arms at both 90% and 70% of V˙O2max (92% +/- 3% vs 85% +/- 6%, P < 0.05 and 90% +/- 3% vs 78% +/- 8%, P < 0.001). This reduction with decreased workload was more pronounced in the arms (-9.8% +/- 7.7% vs -3.2% +/- 3.2%, P < 0.01). EMG(RMS) for the arms was higher, and pole ground contact time was greater than the corresponding values for the legs (both P < 0.01). At both intensities, the blood lactate concentration was higher in the subclavian than that in the femoral vein but was lowered more in the subclavian vein when intensity was reduced (all P < 0.001). CONCLUSIONS The higher muscle activation (percentage of maximal voluntary isometric contraction) in the arms and the longer ground contact time of the poles than the legs contribute to the lower oxygen extraction and elevated blood lactate concentration in the arms in diagonal skiing. The better lactate recovery in the arms than that in the legs is aided by greater reductions in muscle activation and pole force when exercise intensity is reduced.

Biomechanical determinants of oxygen extraction during cross-country skiing

To determine the relationship of muscle activation, force production, and cycle characteristics to O2 extraction during high‐ and lower‐intensity double poling (DP), nine well‐trained male cross‐country skiers performed DP on a treadmill for 3 min at 90% VO2peak followed by 6 min at 70%. During the final minute at each workload, arterial, femoral, and subclavian venous blood were collected for determination of partial pressure of O2, partial pressure of CO2, pH, and lactate. Electromyography (EMG) was recorded from six upper and lower body muscles, leg and pole forces were measured, and cardiorespiratory variables were monitored continuously. O2 extraction was associated with time point of peak pole force (PFpeak), duration of recovery, EMG activity, and lower body use. Arm O2 extraction was lower than in the legs at both intensities (P < 0.001) and was reduced to a lesser extent upon decreasing the workload (P < 0.05). Arm root‐mean‐square EMG was higher during the poling phase and entire cycle compared with the legs (P < 0.001). Blood lactate was higher in the subclavian than in femoral vein and artery (P < 0.001) and independent of intensity. O2 extraction was correlated to low muscle activation, later PFpeak, prolonged poling time, and extensive dynamic lower body use. Cycle rate and recovery time were associated with O2 extraction during high‐intensity exercise only.

Energy system contributions and determinants of performance in sprint cross‐country skiing

To improve current understanding of energy contributions and determinants of sprint‐skiing performance, 11 well‐trained male cross‐country skiers were tested in the laboratory for VO2max, submaximal gross efficiency (GE), maximal roller skiing velocity, and sprint time‐trial (STT) performance. The STT was repeated four times on a 1300‐m simulated sprint course including three flat (1°) double poling (DP) sections interspersed with two uphill (7°) diagonal stride (DS) sections. Treadmill velocity and VO2 were monitored continuously during the four STTs and data were averaged. Supramaximal GE during the STT was predicted from the submaximal relationships for GE against velocity and incline, allowing computation of metabolic rate and O2 deficit. The skiers completed the STT in 232 ± 10 s (distributed as 55 ± 3% DP and 45 ± 3% DS) with a mean power output of 324 ± 26 W. The anaerobic energy contribution was 18 ± 5%, with an accumulated O2 deficit of 45 ± 13 mL/kg. Block‐wise multiple regression revealed that VO2, O2 deficit, and GE explained 30%, 15%, and 53% of the variance in STT time, respectively (all P < 0.05). This novel GE‐based method of estimating the O2 deficit in simulated sprint‐skiing has demonstrated an anaerobic energy contribution of 18%, with GE being the strongest predictor of performance.

The effects of prior high intensity double poling on subsequent diagonal stride skiing characteristics

PurposeTo investigate the influence of prior high intensity double poling (DP) on physiological and biomechanical responses during subsequent diagonal stride (DIA).MethodsEight well-trained male cross-country skiers (age 22 ± 3 yr; VO2max 69 ± 3 ml · kg−1 · min−1) roller-skied on a treadmill sequentially for 3 min at 90% DIA VO2max (DIA1), 3 min at 90% DP VO2peak and 3 min at 90% DIA VO2max (DIA2). Cardio-respiratory responses were monitored continuously and gases and metabolites in blood from the a. femoralis, v. femoralis and v. subclavia determined. Pole and plantar forces and EMG from 6 lower- and upper-body muscles were measured.ResultsVO2 decreased from DIA1 to DP and increased again to DIA2 (both P < 0.05), with no difference between the DIA sessions. Blood lactate rose from DIA1 to DP to DIA2. O2 extraction was attenuated during DP (P < 0.05), but was the same during DIA1 and DIA2. EMGRMS for arm muscles during poling phase, as well as peak pole force and cycle rate were higher, while leg muscle activity was lower during DP than both sessions of DIA (all P < 0.05). The ratio of upper-/whole-body EMGRMS correlated negatively with O2 extraction in the arms during both sessions of DIA (P < 0.05).ConclusionsIn well-trained skiers skiing at high-intensity DP prior to DIA did not influence VO2, muscle activation or forces in the latter. At race intensity DP does not influence the distribution of work between upper- and lower-body during a subsequent bout of DIA. O2 extraction is coupled to technical skills during skiing.

Blood lactate recovery and respiratory responses during diagonal skiing of variable intensity

Abstract The aims of the study were to investigate blood lactate recovery and respiratory variables during diagonal skiing of variable intensity in skiers at different performance levels. Twelve male cross-country skiers classified as elite (n=6; [Vdot]O2max=73±3 ml · kg−1 · min−1) or moderately trained (n=6; [Vdot]O2max=61±5 ml · kg−1 · min−1) performed a 48-min variable intensity protocol on a treadmill using the diagonal stride technique on roller skis, alternating between 3 min at 90% and 6 min at 70% of [Vdot]O2max. None of the moderately trained skiers were able to complete the variable intensity protocol and there was a difference in time to exhaustion between the two groups (elite: 45.0±7.3 min; moderately trained: 31.4±10.4 min) (P<0.05). The elite skiers had lower blood lactate concentrations and higher blood base excess concentrations at all 70% workloads than the moderately trained skiers (all P<0.05). In contrast, [Vdot] E/[Vdot]O2 and [Vdot] E/[Vdot]CO2 at the 70% [Vdot]O2max workloads decreased independently of group (P<0.05). Partial correlations showed that [Vdot]O2max was related to blood lactate at the first and second intervals at 70% of [Vdot]O2max (r=−0.81 and r=−0.82; both P<0.01) but not to [Vdot] E/[Vdot]O2, [Vdot] E/[Vdot]CO2 or the respiratory exchange ratio. Our results demonstrate that during diagonal skiing of variable intensity, (1) elite skiers have superior blood lactate recovery compared with moderately trained skiers, who did not show any lactate recovery at 70% of [Vdot]O2max, suggesting it is an important characteristic for performance; and (2) the decreases in respiratory exchange ratio, [Vdot] E/[Vdot]O2, and [Vdot] E/[Vdot]CO2 do not differ between elite and moderately trained skiers.

Perfusion heterogeneity does not explain excess muscle oxygen uptake during variable intensity exercise

The association between muscle oxygen uptake (VO2) and perfusion or perfusion heterogeneity (relative dispersion, RD) was studied in eight healthy male subjects during intermittent isometric (1 s on, 2 s off) one‐legged knee‐extension exercise at variable intensities using positron emission tomography and a‐v blood sampling. Resistance during the first 6 min of exercise was 50% of maximal isometric voluntary contraction force (MVC) (HI‐1), followed by 6 min at 10% MVC (LOW) and finishing with 6 min at 50% MVC (HI‐2). Muscle perfusion and O2 delivery during HI‐1 (26 ± 5 and 5·4 ± 1·0 ml 100 g−1 min−1) and HI‐2 (28 ± 4 and 5·8 ± 0·7 ml 100 g−1 min−1) were similar, but both were higher (P<0·01) than during LOW (15 ± 3 and 3·0 ± 0·6 ml 100 g−1 min−1). Muscle VO2 was also higher during both HI workloads (HI‐1 3·3 ± 0·4 and HI‐2 4·1 ± 0·6 ml 100 g−1 min−1) than LOW (1·4 ± 0·4 ml 100 g−1 min−1; P<0·01) and 25% higher during HI‐2 than HI‐1 (P<0·05). O2 extraction was higher during HI workloads (HI‐1 62 ± 7 and HI‐2 70 ± 7%) than LOW (45 ± 8%; P<0·01). O2 extraction tended to be higher (P = 0·08) during HI‐2 when compared to HI‐1. Perfusion was less heterogeneous (P<0·05) during HI workloads when compared to LOW with no difference between HI workloads. Thus, during one‐legged knee‐extension exercise at variable intensities, skeletal muscle perfusion and O2 delivery are unchanged between high‐intensity workloads, whereas muscle VO2 is increased during the second high‐intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O2 delivery and uptake. We propose that the excess muscle VO2 during the second high‐intensity workload is derived from working muscle cells.

Metabolic responses and pacing strategies during successive sprint skiing time trials

PURPOSE This study aimed to examine the metabolic responses and pacing strategies during the performance of successive sprint time trials (STTs) in cross-country skiing. METHODS Ten well-trained male cross-country skiers performed four self-paced 1300-m STTs on a treadmill, each separated by 45 min of recovery. The simulated sprint time trial (STT) course was divided into three flat (1°) sections (S1, S3, and S5) involving the double poling subtechnique interspersed with two uphill (7°) sections (S2 and S4) involving the diagonal stride subtechnique. Treadmill velocity and V˙O2 were monitored continuously, and gross efficiency was used to estimate the anaerobic energy supply. RESULTS The individual trial-to-trial variability in STTs performance time was 1.3%, where variations in O2 deficit and V˙O2 explained 69% (P < 0.05) and 11% (P > 0.05) of the variation in performance. The first and the last STTs were equally fast (228 ± 10 s) and ~1.3% faster than the second and the third STTs (P < 0.05). These two fastest STTs were associated with a 14% greater O2 deficit (P < 0.05), whereas the average V˙O2 was similar during all four STTs (86% ± 3% of V˙O2max). Positive pacing was used throughout all STTs, with significantly less time spent on the first than second course half. In addition, metabolic rates were substantially higher (~30%) for uphill than for flat skiing, indicating that pacing was regulated to the terrain. CONCLUSIONS The fastest STTs were characterized primarily by a greater anaerobic energy production, which also explained 69% of the individual variation in performance. Moreover, the skiers used positive pacing and a variable exercise intensity according to the course profile, yielding an irregular distribution of anaerobic energy production.

Near-Infrared Spectroscopy: More Accurate Than Heart Rate for Monitoring Intensity in Running in Hilly Terrain

PURPOSE To investigate the cardiorespiratory and metabolic response of trail running and evaluate whether heart rate (HR) adequately reflects the exercise intensity or if the tissue-saturation index (TSI) could provide a more accurate measure during running in hilly terrain. METHODS Seventeen competitive runners (4 women, V̇O2max, 55 ± 6 mL · kg-1 · min-1; 13 men, V̇O2max, 68 ± 6 mL · kg-1 · min-1) performed a time trial on an off-road trail course. The course was made up of 2 laps covering a total distance of 7 km and included 6 steep uphill and downhill sections with an elevation gain of 486 m. All runners were equipped with a portable breath-by-breath gas analyzer, HR belt, global positioning system receiver, and near-infrared spectroscopy (NIRS) device to measure the TSI. RESULTS During the trail run, the exercise intensity in the uphill and downhill sections was 94% ± 2% and 91% ± 3% of maximal heart rate, respectively, and 84% ± 8% and 68% ± 7% of V̇O2max, respectively. The oxygen uptake (V̇O2) increased in the uphill sections and decreased in the downhill sections (P < .01). Although HR was unaffected by the altering slope conditions, the TSI was inversely correlated to the changes in V̇O2 (r = -.70, P < .05). CONCLUSIONS HR was unaffected by the continuously changing exercise intensity; however, TSI reflected the alternations in V̇O2. Recently used exclusively for scientific purposes, this NIRS-based variable may offer a more accurate alternative than HR to monitor running intensity in the future, especially for training and competition in hilly terrain.

High Intensity Interval Training Leads to Greater Improvements in Acute Heart Rate Recovery and Anaerobic Power as High Volume Low Intensity Training

The purpose of the current study was to explore if training regimes utilizing diverse training intensity distributions result in different responses on neuromuscular status, anaerobic capacity/power and acute heart rate recovery (HRR) in well-trained endurance athletes. Methods: Thirty-six male (n = 33) and female (n = 3) runners, cyclists, triathletes and cross-country skiers [peak oxygen uptake: (VO2peak): 61.9 ± 8.0 mL·kg−1·min−1] were randomly assigned to one of three groups (blocked high intensity interval training HIIT; polarized training POL; high volume low intensity oriented control group CG/HVLIT applying no HIIT). A maximal anaerobic running/cycling test (MART/MACT) was performed prior to and following a 9-week training period. Results: Only the HIIT group achieved improvements in peak power/velocity (+6.4%, P < 0.001) and peak lactate (P = 0.001) during the MART/MACT, while, unexpectedly, in none of the groups the performance at the established lactate concentrations (4, 6, 10 mmol·L−1) was changed (P > 0.05). Acute HRR was improved in HIIT (11.2%, P = 0.002) and POL (7.9%, P = 0.023) with no change in the HVLIT oriented control group. Conclusion: Only a training regime that includes a significant amount of HIIT improves the neuromuscular status, anaerobic power and the acute HRR in well-trained endurance athletes. A training regime that followed more a low and moderate intensity oriented model (CG/HVLIT) had no effect on any performance or HRR outcomes.

Using bilateral functional and anthropometric tests to define symmetry in cross-country skiers

Abstract The aim of this study was to evaluate the symmetry of anthropometry and muscle function in cross-country skiers and their association to vertical jumping power. Twenty cross-country skiers were recruited (21.7 ± 3.8 yrs, 180.6 ± 7.6 cm, 73.2 ± 7.6 kg). Anthropometric data was obtained using an iDXA scan. VO2max was determined using the diagonal stride technique on a ski treadmill. Bilateral functional tests for the upper and lower body were the handgrip and standing heel-rise tests. Vertical jump height and power were assessed with a counter movement jump. Percent asymmetry was calculated using a symmetry index and four absolute symmetry index levels. At a group level the upper body was more asymmetrical with regard to lean muscle mass (p = 0.022, d = 0.17) and functional strength (p = 0.019, d = 0.51) than the lower body. At an individual level the expected frequencies for absolute symmetry level indexes showed the largest deviation from zero for the heel-rise test (χ2 = 16.97, p = 0.001), while the leg lean mass deviated the least (χ2 = 0.42, p = 0.517). No relationships were observed between absolute symmetry level indexes of the lower body and counter movement jump performance (p > 0.05). As a group the skiers display a more asymmetrical upper body than lower body regarding muscle mass and strength. Interestingly at the individual level, despite symmetrical lean leg muscle mass the heel-rise test showed the largest asymmetry. This finding indicates a mismatch in muscle function for the lower body.