The influence of physiobiomechanical parameters, technical aspects of shooting, and psychophysiological factors on biathlon performance: A review

4.1. The demands of biathlon skiing

Skiing time during a biathlon varies from approximately 15 min in the sprint to approximately 45 min in individual competitions. During this skiing, the heart rate (HR) is approximately 90% of maximal HR (HR_max), decreasing slightly as the shooting station is approached and decreasing to approximately 70% and 60% of HR_max while shooting in the prone and standing positions, respectively.² Since the introduction of the skating technique in the 1980s, biathlon skiing speed, like cross-country skiing speed,⁷ has increased to become approximately 7% faster at present than during the 2001/2002 season⁶ (Fig. 3). Today, the average skiing speeds of the 10 best biathletes in World Cup biathlon sprint competitions are 7.2 m/s for male and 6.3 m/s for female atheletes.⁸

It should be noted that these averages are confounded by various factors, such as the location of the event and weather during the competition. Indeed, racing time is prolonged by 2% for every 1000-m increase in altitude, 5% per 1% increase in incline, 1%–2% per 1 m/s elevation in wind speed, and 2%–4% when changing from packed snow to softer snow.⁹ The increments in average speed may be due in part to alterations in training regimens (e.g., training for upper body strength and endurance, speed, and technique), as in the case of cross-country skiers,10, 11, 12, 13 but also to improvements in skis and waxes as well as preparation of the course/snow and skis. These increases in skiing speed may also change the physiological and biomechanical requirements for effective biathlon skiing, a topic that requires further investigation.

Luchsinger et al.⁸ showed recently that approximately 60% of overall performance in biathlon sprint competitions is determined by skiing speed. However, in individual competitions, where each shot missed results in a 1-min penalty, shooting performance is probably more important. However, the impact of skiing speed, shooting time, shooting accuracy, and, potentially, tactics, as well as pacing on overall performance in pursuit and mass start competitions, is currently unknown.

4.2. Different skiing subtechniques

In the modern biathlon, skating is the only skiing technique used. As in cross-country skiing, this skating encompasses several gears (subtechniques), with which the biathlete adapts to the skiing speed and terrain.¹⁴ In general, lower gears are used on uphill sections and at slower velocities and higher gears are used on flatter and downhill sections and at higher speeds.

In the case of cross-country skiing, Gears 2 and 3 (sometimes also referred to as V1 and V2) are used most frequently.¹⁵ Gear 1 is used only on very steep uphill terrain during training. Gear 2, used solely on uphill terrain, involves nonsymmetrical poling in combination with work by the legs, whereas Gear 3 (symmetrical poling with leg work) is usually applied on moderate uphill or even on flat terrain. The proposal that the time spent on uphill sections is the most important determinant of the finishing time of a cross-country skier¹⁶ emphasizes the key importance of Gears 2 and 3.

4.3. Determinants of biathlon skiing performance

A biathlon competition consists of 3 or 5 high-intensity bouts of skiing, each lasting 5–8 min depending on the type of competition,⁶ and separated by a short break (approximately 25–30 s) while preparing and performing the shooting. Therefore, the biathlon is classified as an endurance sport, where the impact of aerobic energy metabolism on overall performance is significant.¹⁷ More generally, endurance performance depends on both aerobic and anaerobic factors, together with exercise economy and/or gross mechanical efficiency.17, 18 It has been proposed that the 56-km classical cross-country skiing race results in both peripheral and central fatigue,¹⁹ whereas for a shorter race (e.g., simulated sprint competition) the fatigue may be only peripheral.²⁰ Thus, in the case of the biathlon, both peripheral and central fatigue may be experienced and affect both skiing performance and shooting accuracy.

In one of the few studies performed on biathlon skiing to date, Rundell and Bacharach²¹ showed that peak oxygen uptake (VO_2peak) correlated with skiing time during the 20-km competition, but only for males. In another investigation, Rundell²² found that maximal oxygen consumption (VO_2max) and the lactate threshold exhibit moderate correlations with roller skiing performance by female biathletes. Similar results have been reported for both female²³ and male²⁴ cross-country skiers, for whom gross mechanical efficiency is also related to performance.²⁵

Because the best biathletes can also compete in cross-country skiing at an elite international level, the requirements for aerobic capacity made by these 2 disciplines are likely to be similar. This comparison is summarized in Table 1. Taken together, these findings indicate that a high VO_2max, lactate threshold, and gross efficiency are essential for successful biathlon skiing performance. However, in the biathlon, as in cross-country skiing, uphill sections require power output higher than the VO_2max,26, 27, 28, 29 which, together with the increasing average speeds, indicates that the anaerobic component is also a crucial determinant of performance.

In biathlon, carrying a rifle on the back while skiing increases O₂ consumption, HR, ventilatory responses, and blood lactate concentration, as well as accelerating the cycle rate and requiring more pronounced leg work.4, 30 This finding is especially true for females, who typically weigh less than male, but carry a rifle of the same weight. However, data regarding the effects of carrying a rifle on biathlon skiing performance remain highly limited. Thus, it is of considerable interest to clarify these effects on, for example, skiing position (range of motion of the different joints), as well as the choice and use of different gears (subtechniques), including consideration of potential sex differences.

5.1. Postural balance

Studies on rifle, pistol, and biathlon shooting have focused on postural balance in the standing situation and have shown stance stability to be a key factor for successful performance. Elite male and female shooters show less body sway than nonelite shooters,35, 36, 37, 38, 39, 40 and this clearly distinguishes high-level from low-level shooters.32, 33,41, 42, 43, 44, 45 Accordingly, Era et al.³⁷ have recommended specific balance training, primarily for young and inexperienced shooters. Moreover, biomechanical biofeedback can also improve the postural stability of top-level shooters.⁴⁶

At the same time, specific shooting stances may also improve stability. In this context, it has been shown that standing at an angle of 15° to the line of fire results in the best overall performance by air pistol shooters. However, positioning when shooting a rifle differs, and, in general, few kinematic studies on shooting positions have been reported.⁴⁷ In contrast with competitive rifle shooters, the biathlete has very limited time in which to find the optimal position, making the relationship between shooting position and performance particularly important in this context.

Previous investigations on biathlon32, 33,⁴⁸ and rifle shooting39, 49 have revealed a pronounced relationship between body sway and motion of the rifle. In other words, poor stance stability is associated with an unstable hold on the rifle, which results in poor and variable shooting.32, 36,³⁹

With respect to stance, the anteroposterior (AP) direction (across the line of fire) is the best predictor of shooting scores³³ and clearly distinguishes experienced shooters from novices.32, 37 Moreover, body sway in the AP direction is significantly higher than in the mediolateral (ML) direction (along the line of fire).32, 40,⁵⁰ In the case of biathlon shooting, muscle fatigue increases ankle joint motion, resulting in more pronounced destabilization in the AP than in the ML direction.³³

In general, posture is destabilized by exercise51, 52, 53 and metabolic activation, with increases in both heart and breathing rate under aerobic and anaerobic load.54, 55 Furthermore, comprehensive training designed to improve coordination, strength, range of motion, and reaction to proprioceptive demands strengthens balance.⁵⁶ Such training and the resultant development of hip/ankle strategies⁵¹ might explain the differences in the stance stability of high-level and young biathletes after an intense physical load.³³ In any case, the well-recognized negative effect of physical exercise (e.g., on roller skis, a bicycle, or skis) on postural balance31, 40,57, 58, 59 is of fundamental importance in connection with biathlon shooting. In this context, Sattlecker et al.⁵⁸ have demonstrated that lower body work exerts a greater negative impact on stance stability than upper body exercise.

Prone shooting is also influenced by the more rapid breathing and HR caused by exercise,⁶⁰ but to a lesser extent than shooting in the standing position.⁶¹ As mentioned, the HR declines as the biathlete stops skiing and commences shooting. During shooting, it is usually 60%–70% of HR_max if standing and even lower during prone shooting² owing to reactivation of cardiac parasympathetic nerves.⁶² Tharion et al.⁶⁰ have reported that in the prone position the HR slows even faster because of the more pronounced improvements in blood and oxygen supply to the brain.

5.2. Rifle stability

Rifle stability, an important determinant of high-level performance in both biathlon shooting and several other shooting disciplines, is closely related to shooting scores while standing39, 41,43, 63 and distinguishes high- from low-scoring male and female athletes.32, 33,43, 45,64, 65 Moreover, extensive vertical sway exerts a negative effect on shooting accuracy at rest.45, 66 Ihalainen et al.⁴⁸ discovered cleanness of triggering (i.e., the motion of aiming point 0–0.2 s before the shot) and, once again, vertical stability of hold to be the most important determinants of shooting performance at rest and under load conditions.⁴⁸ In contrast, changes in air rifle shooting performance from training to competition were most strongly related to alterations in the horizontal hold on the rifle.⁴⁹

Differences in the athlete's level of skill and the particular discipline involved (air rifle vs. running target shooting) may explain at least some of the discrepancies between these reports. In running target shooting, the athlete must follow the target in the horizontal direction, and therefore the ability to stabilize the rifle in the vertical direction is essential. In connection with air rifle shooting, as well as biathlon shooting,⁵⁷ horizontal movement is the major factor that discriminates high- from low-level athletes. This may reflect the relationship between rifle and body sway; Sattlecker et al.³² found a strong relationship between displacement of the center of mass in the AP direction and horizontal rifle sway. In general, previous physical exercise exerts a negative influence on how the rifle is held during biathlon shooting in the standing position,31, 33 increasing the movement of the rifle by as much as 50%, with the rising center of pressure after a physical load indicating the interrelationship between these 2 variables.³³

In the case of prone shooting, Hoffman et al.³¹ observed only minimal effects of exercise intensity on rifle stability, whereas Sattlecker et al.³³ found the vertical sway of the barrel to be the main predictor of prone performance after physical exercise. The recent alterations in breathing and aiming strategies required by more rapid shooting may explain at least some of the differences between these 2 studies.

In general, specific holding and relaxation training can improve rifle stability and thereby improve shooting accuracy.67, 68 Furthermore, biomechanical biofeedback has been reported to improve the barrel stability of high-level shooters.⁴⁶ To extend our understanding of the significance of rifle positioning, future investigations in this area should combine kinematic with kinetic analyses.

5.3. Shoulder forces

The butt plate of the rifle should be fixed against the shoulder and held isometrically by the elbow flexors.⁶¹ A stock of optimal length⁶⁹ and substantial contact between the rifle and shoulder⁷⁰ improve the hold on the rifle. Moreover, holding the rifle butt tightly against the shoulder results in better horizontal rifle stability.³³ Previous physical exercise often results in lower rifle forces on the shoulder, attenuating the stability of the rifle, particularly when shooting in the prone position.33, 70 Thus, fatigued elbow flexors may produce lower shoulder forces, thereby impairing rifle hold and accuracy.⁶¹ More detailed knowledge concerning shoulder forces should help trainers and athletes to find the optimal rifle length and ideal shape of the butt plate.

5.4. Triggering

The fine motor control involved in triggering during biathlon⁴¹ and other types of shooting has scarcely been examined, even though it has been argued that triggering behavior is a major predictor of biathlon shooting performance.71, 72 Moreover, trigger forces before shooting at rest while standing were higher in elite male and female athletes compared to young biathletes.⁷³ In general, physical exercise before shooting decreased trigger forces,⁵⁷ at least for low-scoring biathletes, but not for high-scoring male and female biathletes.⁵⁷ The appropriate timing of finger movement was impaired by fatigue, an effect that could be compensated for by new patterns of motor coordination.⁷⁴ Thus, in contrast with young athletes, elite biathletes might have developed motor strategies that allow precise neural control of the distal joints and consistent triggering behavior, even when fatigued. Furthermore, Sattlecker et al.³³ observed moderate correlations between triggering behavior and rifle stability during prone shooting. These findings highlight the importance of triggering in connection with biathlon shooting, but detailed and systematic investigations on this topic are sorely needed.

6.1. Cardiac activity and shooting

Konttinen et al.⁷⁷ observed a decrease in HR before triggering by both elite and nonelite male shooters. Basing their reasoning on the intake-rejection hypothesis,⁸⁸ these authors proposed that this decrease reflects an outward-directed attentional focusing, although the extent of the decrease was not associated with shooting scores. Moreover, Helin et al.⁷⁶ demonstrated that elite male and female shooters pull the trigger during diastole (when the heart ventricles are relaxed and filling), with beginners firing during both diastole and systole, with better results during diastole.

Upon examining the cardiac cycle in greater detail, Konttinen et al.⁸⁹ found that nonelite male rifle shooters performed above average when they shot during the initial 0–50% or final 70%–99% of the R-R interval (the period between adjacent heartbeats). These authors argued that the “critical factor is not the heart relaxation, but the mechanical movement caused by the heart muscle contraction” (p. 400). This movement reaches its maximum between 400 and 600 ms through 1 cycle, which corresponds with approximately 51%–69% of the R-R interval. These observations are in contrast to those of Mets et al.,⁹⁰ who found no relationship between the timing of triggering within the cardiac cycle and shooting performance by elite junior male and female rifle shooters. Clearly, further study designed to clarify the optimal timing of shooting is required.

In the case of biathlon shooting, it is assumed that the timing of the shot within the cardiac cycle is probably more influential than with sport shooting because of the pronounced cardiovascular load of the preceding skiing, which perturbs visuomotor control and psychomotor regulation. Accordingly, biathletes may benefit from biofeedback that promotes triggering during the R-R interval of a cardiac cycle, as proposed by Mets et al.⁹⁰ Of additional importance is the decrease in shooting time (the time between entering and leaving the shooting mat) that has occurred during the last few decades. For example, the average shooting time for the 10 best male biathletes in the 20-km individual competition was 27.9 s at the World Championships in 2017⁹¹ vs. 33.5 s in 1997⁹². The question then arises as to whether more rapid triggering alters the optimal placement of the shot within the R-R interval and in relation to breathing.

6.2. Cortical activity and shooting

In numerous articles, Konttinen et al.42, 64,79, 82,93, 94 have evaluated the slow brain waves of shooters 7.5 s before and 1.5 s after pulling the trigger. Before the shot, slow brain potentials decrease monotonically until the trigger is pulled,⁸² and this phenomenon is enhanced by aiming and attenuated by holding the rifle for stability. In line with these findings, these investigators reported that, in connection with successful shots by both experienced elite and subelite male shooters,⁹⁴ frontal positivity is an indicator of motor activity, whereas right-sided negativity reflects visuospatial processing. Consequently, they concluded that slow brain potentials provide information concerning the optimal balance between aiming and motor processes, information that may be of value in connection with diagnostic approaches.

Spectral analyses, most of which have focused on the alpha band at 8–12 Hz, have demonstrated that experienced right-handed male and female shooters with an ipsilateral hand-eye dominance exhibited a larger band (indicative of less activation) in the left temporal area than the right hemisphere during the preshot phase.⁷⁸ This finding, since confirmed several times,^81,95, 96, 97 has been interpreted as less pronounced verbal and analytical processes in experienced shooters than in novices.⁹⁶ With respect to the visual domain, Loze et al.⁹⁷ detected a larger occipital alpha band before best shots, suggestive of more pronounced suppression of visual attention than before worst shots. These authors argued that excessive visual attention might interfere with the motor program involved in automatic aiming, which is controlled by mechanisms of intention. Thus, in the context of the biathlon, visualization of one's own and/or an opponent's performance may have a negative impact on shooting.

Functional changes in the electroencephalogram (EEG) can be quantified as the percentage change in signal strength before the shot. Increases and decreases are referred to as event-related synchronization (ERS) and event-related desynchronization (ERD), respectively.⁹⁸ Applying this approach to the entire scalp, Del Percio et al.⁹⁹ observed less ERD in the low (8–10 Hz) and high (10–12 Hz) regions of the alpha band of elite male and female shooters during the preparatory phase in comparison with nonathletes. In association with the best shots of elite athletes, the ERS at high α frequencies was enhanced, specifically at the right and parietal sites. The neural efficiency hypothesis¹⁰⁰ postulates lower global activation in athletes than in nonathletes, as well as a specific ERS pattern localized to certain regions of the brain during successful shots.

Another approach, EEG coherence analysis, addresses functional communication between different areas of the brain on the basis of correlations in the amplitudes of signals of a given frequency at 2 locations.¹⁰¹ High coherence indicates communication, whereas low coherence reflects regional autonomy or independence.¹⁰² Upon analyzing the low alpha, high alpha, and low beta band frequencies, Deeny et al.¹⁰¹ found that expert male and female shooters showed less corticocortical communication than skilled shooters, which was interpreted as reduced cognitive involvement in aiming. A subsequent investigation provided evidence that cortical networks become more refined as expertise is gained.¹⁰³

Few such studies have focused on the theta band at 4–8 Hz,84, 96 which is associated with concentration¹⁰⁴ and internalized attention.¹⁰⁵ Doppelmayr et al.⁸⁴ demonstrated a continuous increase in the amplitude of this theta band in the frontal midline region (Fmθ) during the 3 s immediately before shooting by male experts, but not novices whose shooting was significantly less accurate. These researchers concluded that experts and novices use different aiming strategies, with enhanced attentional focus on triggering by the experts only.

6.3. Gaze behavior and shooting

Upon comparing the gaze behavior and cortical activity of expert and nonexpert shooters, Janelle et al.⁸¹ detected more prolonged fixation on the target immediately before the shot by the experts. This gaze strategy, termed quiet eye,¹⁰⁶ is considered to be an objective measure of visuomotor control, influencing attentional control, response programming, and external focus.¹⁰⁷

6.4. Studies specifically on biathlon shooting

Our search of PubMed on March 3, 2018, revealed only 3 psychophysiological investigations of biathlon shooting, specifically on the impact of preceding physical load on rifle shooting. Vickers and Williams³ analyzed the physiological arousal, cognitive anxiety, and gaze behavior of 10 male and female members of national junior and senior biathlete teams while shooting at rest and after exercise at 55%, 70%, 85%, or 100% of their VO_2max and under low or high psychological pressure. After exercise at 100%VO_2max, 58% of the adjusted difference between low- and high-pressure scores could be accounted for by the duration of the quiet eye and ratings of perceived exertion. After such a maximal load, biathletes who performed well even under high pressure (nonchokers) maintained their quiet eye longer under high than low pressure. Thus, by focusing visual attention on the target, biathletes might be able to avoid choking, even after a high physical load and when under stress.

Luchsinger et al.⁸⁶ reported that male and female biathletes exhibited better shooting performance and had higher Fmθ (frontal-midline theta activity) than cross-country skiers, both when shooting without preceding physical load and after 6-min bouts of roller ski skating at 85% of HR_max. In addition, submaximal exercise exerted no effect on the shooting accuracy or Fmθ of either biathletes or cross-country skiers, which, it was argued, may have been due to their considerable fitness. In another EEG analysis of Fmθ and α activity in young male and female biathletes, Gallicchio et al.⁸⁷ found that shooting accuracy with no preceding load and after 3 min of cycling at 90% of HR_max was the same. In contrast with the observations of Luchsinger et al.,⁸⁶ Fmθ was lower with preceding loading than without. This discrepancy may be explained by the differences in age and level of fitness of the participants and the different physical loads applied, which might have influenced focused attention.

Moreover, the magnitude of the α band over the temporal and occipital, but not the central, regions can be elevated, indicating a compensatory strategy for maintaining shooting performance even after intense cardiovascular load. Better performance after loading was associated with higher Fmθ and less intense left central and higher left temporal α bands.⁸⁷ These findings support the conclusion that neural efficiency, as indicated by prolonged inhibition of regions of the brain not involved in movement and activation of those involved, is beneficial to biathlon shooting.

Altogether, these findings indicate that a successful biathlete must have good body perception and self-regulation to anticipate the optimal time point for shooting. This time point seems to be related to the cardiac cycle and a continuous increase in attention (as indicated by the Fmθ) before triggering. Accordingly, it has been proposed that appropriate biofeedback could improve the shooting performance of biathletes.