Gertjan Ettema

Norwegian University of Science and Technology | NTNU · Department of Neuroscience (INM)

The purpose of this study was to examine the influence of tactical positioning on performance in the heats of sprint cross-country (XC) skiing among men and women and the consistency of overtaking events over repeated competitions on the same racecourse. Thirty male and thirty female elite to world-class level skiers within each competition [(sprin...

In cross-country skiing, athletes use different techniques akin to locomotor gaits such as walking and running. Transitions between these techniques generally depend on speed and incline, in a similar way as walk-run transitions. Previous studies have examined the roles of incline, speed, and mechanical power demand in triggering transitions. Howev...

The purpose of this study was to examine the influence of race tactics for performance in the heats of an international sprint crosscountry (XC) skiing competition in the classical style. Thirty elite male XC skiers (age: 24±3 years, sprint International Ski Federation [FIS] points: 61±27) performed a sprint time-trial (STT) followed by one to thre...

We investigated the notion that ergometer rowing technique at different intensities, but self-chosen stroke rates (SR) would resemble each other more than when rowing at other intensity-SR combinations. Twelve competitive male rowers performed ergometer rowing at three intensities x three SR, including the self-chosen one. Kinetics were recorded an...

Aim The purpose of this study was to examine the influence of race tactics on performance in the heats of an international sprint crosscountry (XC) skiing competition in the classical style. Methods Thirty elite male XC skiers (age: 24±3 years, sprint [FIS] points: 61±27) performed a sprint time-trial (STT) followed by one to three heats on a 1.7 k...

The purpose of this investigation was to compare how key variables of the steady glide phase relate to performance in the two hill sizes used in World Cup and Olympic competitions, i.e, normal and large hills. In this study, 38 and 33 jumps of elite ski jumpers were measured with a differential global navigation satellite system (dGNSS) on a normal...

The purpose of this study was to find a generic method to determine the aerial phase of ski jumping in which the athlete is in a steady gliding condition, commonly known as the ‘stable flight’ phase. The aerial phase of ski jumping was investigated from a physical point mass, rather than an athlete–action-centered perspective. An extensive data col...

Purpose: To investigate the interaction between exercise modality (i.e., upper- and lower-body exercise) and sex in physiological responses and power output (PO) across the entire intensity spectrum (i.e., from low to maximal intensity). Methods: Ten male and 10 female cross-country (XC) skiers performed a stepwise incremental test to exhaustion co...

The ventilatory threshold (VT) separates low- from moderate-intensity exercise, the respiratory compensation point (RCP) moderate- from high-intensity exercise. Both concepts assume breakpoints in respiratory data. However, the objective determination of the VT and RCP using breakpoint models during upper-body modality exercise in wheelchair athlet...

This study investigated the explanatory power of a sensor fusion of two complementary methods to explain performance and its underlying mechanisms in ski jumping. A differential Global Navigation Satellite System (dGNSS) and a markerless video-based pose estimation system (PosEst) were used to measure the kinematics and kinetics from the start of t...

Objectives The aim of this study was to examine the effect of speed on mechanical energy fluctuations and propulsion mechanics in the double-poling (DP) technique of cross-country skiing. Methods Kinematics and dynamics were acquired while fourteen male skiers performed roller-skiing DP on a treadmill at increasing speeds (15, 21 and 27 km∙h ⁻¹ )....

The purposes of this study were: 1) to investigate the anaerobic energy contribution during a simulated crosscountry (XC) skiing mass-start competition while roller-ski skating on a treadmill; 2) to investigate the relationship between the recovery of the anaerobic energy reserves and performance; and 3) to compare the gross efficiency (GE) method...

Paralympic rowers with functional impairments of the legs and trunk rely on appropriate seat configurations for performance. We compared performance, physiology, and biomechanics of an elite Paralympic rower competing in the PR1 class during ergometer rowing in a seat with three different seat and backrest inclination configurations. Unlike able-bo...

This study aims to investigate the inrun position in ski-jumping, in search for factors increasing the inrun speed without compromising the take-off. The inrun position of eight World Cup (WC) and fifteen Continental Cup (COC) ski jumpers were investigated in a wind tunnel at NTNU. A preferred position, replicating a jumper’s position in competitio...

Purpose: To provide novel insight regarding the influence of exercise modality on training load management by: 1) providing a theoretical framework for the impact of physiological and biomechanical mechanisms associated with different exercise modalities on training load management in endurance exercise, and 2) comparing effort-matched low-intensit...

Our primary aim was to explore the development of player load throughout match time (i.e., the pattern) using moving 5-min windows in an elite soccer team and our secondary aim was to compare player load patterns between different positions within the same team. The dataset included domestic home matches (n = 34) over three seasons for a Norwegian...

Purpose: Biathlon is an Olympic sport combining 3-5 laps of cross-country skiing with rifle shooting, alternating between the prone and standing shooting positions between laps. The individual distance and the sprint are extensively examined whereas the pursuit, with start times based on the sprint results, is unexplored. Therefore, the current st...

Introduction: Variable power output (VP) is one of the main characteristics of a road cycling mass-start. Tolerating VP during outdoor road cycling highly influences performance. There is a lack of continuous and comprehensive measurements during this power condition. Accordingly, the aim of the present study was to investigate physiological respon...

Introduction In cycling, the utilization of the drops position (i.e. the lowest handlebar position relative to the ground) allows for reduced frontal area, likely improved aerodynamics and thus performance compared to the tops (i.e. the position producing the most upright trunk). The reduced trunk angle during seated submaximal cycling has been sho...

Cross-country skiers use different sub-techniques like ‘gears’ (diagonals stride, double poling with kick, and double poling) depending on terrain (incline) and demand (speed and external work rate). Previous studies have identified the major effect of speed and incline, but not any potential interaction between these parameters: the incline-speed...

Imitation jumps are frequently used in training for ski jumping. Yet, the dynamics of these jumps differ considerably. Thus, the relevance of imitation jumps for ski jumping performance is not elucidated. The aim of this study was to investigate the relationship between the technical execution of imitation jumps and ski jumping performance level. W...

Background: Cycling competitions are often of long duration and include repeated high-intensity efforts. Purpose: To investigate the effect of repeated maximal sprints during 4 hours of low-intensity cycling on gross efficiency (GE), electromyography patterns, and pedaling technique compared with work-matched low-intensity cycling in elite cycli...

This study examined the potential trade-off in performance between maximum physical capabilities in the handball jump throw, a fundamental skill comprised of two mechanically independent tasks. Elite handball players performed jump throw actions from a force plate for each of three instructions: jump at maximum capability, throw at maximum capabili...

In this review, we examine the literature in light of the mechanical principles that govern linear accelerated running. While the scientific literature concerning sprint mechanics is comprehensive, these principles of fundamental mechanics present some pitfalls which can (and does) lead to misinterpretations of findings. Various models of sprint me...

PURPOSE: To investigate fluctuations in speed, work rate and heart rate (HR) when cross-country (XC) ski skating across varying terrain at different endurance training intensities. METHODS: Seven male Norwegian junior skiers performed maximal speed (Vmax) tests in both flat and uphill terrain. Thereafter, 5-km sessions at low- (LIT), moderate- (MI...

Objectives The purpose of this study was to investigate the effect of different incline-speed combinations, at equal external power outputs, on the mechanics and energetics of the double-poling (DP) technique in cross-country skiing.Methods Fourteen elite male cross-country skiers performed treadmill DP on roller-skis at low, moderate, and high mea...

Background The effect of cadence and work rate on the joint specific power production in cycling has previously been studied, but research has primarily focused on cadences above 60 rpm, without examining the effect of low cadence on joint contribution to power. Purpose Our purpose was to investigate joint specific power production in recreational...

Dataset for the present publication. (CSV)

Individual data for the current paper on mechanical energetics and dynamics in uphill double poling. (XLSX)

The performance of the take-off in ski jumping creates high demands on the athlete’s neuromuscular system and is associated with the length of the jump. However, investigations of muscle activity during take-off are limited to a few qualitative analyses as summarized by Schwameder (2008). A principal component analysis (PCA) can quantify relevant a...

Purpose: To investigate the contribution from maximal speed (Vmax) and %Vmax to the finish sprint speed obtained in a cross-country sprint in the classical and skating style, as well as the coinciding changes in kinematic patterns and the effect of pacing strategy on the %Vmax. Methods: Twelve elite male cross-country skiers performed two 80-m Vmax...

Purpose The aim of this study was to investigate the effect of exhaustive exercise on technique preference and the accompanying physiological response during classic skiing at constant workload, but with varying incline–speed combinations. Methods Seven male competitive cross-country skiers performed four tests, each lasting 23 min, at constant 20...

Objectives The primary aim was to compare physiological and perceptual outcome parameters identified at common gas exchange and blood lactate (BLa) thresholds in Paralympic athletes while upper-body poling. The secondary aim was to compare the fit of the breakpoint models used to identify thresholds in the gas exchange thresholds data versus contin...

VE/VO2 and VE/VCO2 plots fitted with two regression lines. The data is of the six or seven completed stages of each of the 15 athletes. Breakpoint presence is indicated above each individual plot. Furthermore, it is indicated in the second row above the figures whether the two thresholds occur at the same time, or the VE/VO2 occurs before or after...

Data. Data and analyses conducted in this study of gas exchange and blood lactate threshold in Paralympic sitting athletes. (XLSX)

Purpose: To compare peak oxygen uptake (VO2peak) and exercise efficiency between upper-body poling (UBP) and arm crank ergometry (ACE) in able-bodied (AB) and paraplegic participants (PARA). Methods: Seven PARA and eleven AB upper-body trained participants performed four 5-min submaximal stages, and an incremental test to exhaustion in UBP and A...

Biathlon is an Olympic winter sport where rifle shooting and cross-country skiing is combined in various race formats. In the individual distance (15 km for women and 20 km for men), athletes compete over five laps of skiing with shooting between each lap (i.e., 4 shootings). The aim of the current study was to compare total race time differences,...

McGhie, D, Østerås, S, Ettema, G, Paulsen, G, and Sandbakk, Ø. Strength determinants of jump height in the jump throw movement in women handball players. J Strength Cond Res XX(X): 000-000, 2018-The purpose of the study was to improve the understanding of the strength demands of a handball-specific jump through examining the associations between ju...

The purpose of the present study was to examine the influence of increased loading of the roller ski on metabolic cost, gross efficiency, and kinematics of roller ski skating in steep and moderate terrain, while employing two incline-specific techniques. Ten nationally ranked male cross-country skiers were subjected to four 7-minute submaximal inte...

Excel file containing data presented in the results chapter. (XLSX)

The purpose of this study was to examine the effect of increasing exercise intensity on the role of joint powers in ergometer double poling (DP), while taking specific dynamic constraints into account. One main question was whether lower-body power contribution increased or decreased with increasing intensity. Nine male Norwegian national-level cro...

Cross-country skiers change technique depending on terrain (incline) and effort (work rate; speed at a particular incline or resistance). The literature is not unequivocal about the influence of incline or speed on the choice of technique, i.e., which of these act as a 'control parameter'. Identifying task related control parameters for spontaneous...

Biathlon is an Olympic sport combining cross-country skiing with the skating technique and rifle shooting. The sprint (7.5 km for women and 10 km for men) includes two shootings between the three laps of skiing. The aims of the current study are to compare biathletes of different performance-levels and sex on total race time and performance-determi...

Practitioners have for many years argued that athletic sprinters should optimise front-side mechanics (leg motions occurring in front of the extended line through the torso) and minimise backside mechanics. This study aimed to investigate if variables related to front-and backside mechanics can be distinguished from other previously highlighted kin...

The aims of this study were to i) quantify the magnitude of kinematic stride cycle asymmetry in high-level athletic sprinters, ii) explore the association between kinematic asymmetry and maximal sprint running performance, and iii) investigate possible associations between kinematic asymmetry and injury prevalence. Twenty-two competitive sprinters...

Background Nordic combined (NC) is an Olympic winter-sport performed as a ski jumping (SJ) event followed by a cross-country (XC) pursuit race employing the skating style. Purpose To elucidate the associations between sport-specific laboratory capacities and SJ, XC skiing, and overall NC performance in a world-cup NC event. Methods Twelve interna...

This study compared the effects of adding upper-body sprint-intervals or continuous double poling endurance training to the normal training on maximal upper-body strength and endurance capacity in female cross-country skiers. In total, 17 female skiers (age: 18.1±0.8yr, body mass: 60±7 kg, maximal oxygen uptake (VO2max): 3.30±0.37 L.min⁻¹) performe...

Supporting data. (XLSX)

In classical cross-country skiing, diagonal stride (DIA) is the major uphill sub-technique, while double poling (DP) is used on relatively flat terrain. Although, the dependence of incline and speed on the preference of either sub-technique seems clearly established, the mechanisms behind these preferences are not clear. Therefore, the purpose of t...

The purpose of the present study was to investigate the effect of cadence on joint specific power and cycling kinematics in the ankle joint in addition to muscle oxygenation and muscle VO2 in the gastrocnemius and tibialis anterior. Thirteen cyclists cycled at a cadence of 60, 70, 80, 90, 100 and 110 rpm at a constant external work rate of 160.1 ±...

Previous publication from the same experiment. (PDF)

Dataset for the present publication. (XLSX)

In Norway, approximately 10% (574.000) of the population have a disability and of these 8% (50.000) are estimated to be wheelchair bound, every tenth person (5000) due to a spinal cord injury (SCI). As compared to the general able-bodied population, risk of morbidity and mortality is increased in persons with a SCI. The most common cause of death i...

Accelerated running is characterised by a continuous change of kinematics from one step to the next. It has been argued that breakpoints in the step-to-step transitions may occur, and that these breakpoints are an essential characteristic of dynamics during accelerated running. We examined this notion by comparing a continuous exponential curve fit...

Excel File containing all step data that the curve fitting analysis is based on. (XLSX)

Purpose: The present study investigates the effect of cadence on joint specific power and oxygenation and local muscle oxygen consumption in the vastus lateralis and vastus medialis in addition to the relationship between joint specific power and local muscle oxygen consumption (mVO2). Methods: Seventeen recreationally active cyclists performed...

The purposes of the current study were to 1) test if the hinge position in the binding of skating skis has an effect on gross efficiency or cycle characteristics and 2) investigate whether hinge positioning affects synergistic components of the muscle activation in six lower leg muscles. Eleven male skiers performed three 4-min sessions at moderate...

Background: Previous studies using electroencephalography (EEG) to monitor brain activity have linked higher frontal theta activity to more focused attention and superior performance in goal-directed precision tasks. In biathlon, shooting performance requires focused attention after high-intensity cross-country skiing. Purpose: To compare biathl...

Purpose: To characterize gender differences in power output, energetic capacity and exercise efficiency during whole-body (WP), upper-body (UP), and arm poling (AP). Methods: Ten male and ten female elite cross-country skiers, matched for international performance level, completed three incremental submaximal tests and a 3-min self-paced perform...

The purpose of the present study was to examine the effects of external work rate on joint specific power and the relationship between knee extension power and vastus lateralis muscle oxygen consumption (mVO2). We measured kinematics and pedal forces and used inverse dynamics to calculate joint power for the hip, knee and ankle joints during an inc...

Maximal oxygen uptake (VO2max) is regarded as the most performance-differentiating physiological measure in cross-country (XC) skiing. In addition, upper-body strength and lean mass have been associated with double poling (DP) power in XC skiers. In this study, we tested upper-body maximal strength, lean mass and VO2max’s contributions to predict D...