A Flight Helmet-Attached Force Gauge for Measuring Isometric Neck Muscle Strength.

INTRODUCTION: Fighter pilots must withstand high Gz-forces that can damage the cervical spine. Strength of the cervical musculature is of vital importance when it comes to preventing these G-induced neck injuries. However, there is very little evidence on valid neck muscle strength measurement methods for fighter pilots. The aim of this study was to examine the validity of a commercial force gauge attached to a pilot's helmet for measuring isometric neck muscle strength.METHODS: A total of 10 subjects performed maximal isometric cervical flexion, extension, and lateral flexion with the helmet-attached gauge and with a weight stack machine, which was used as a reference. Electromyography (EMG) activities were recorded from the right and left sternocleidomastoids and cervical erector spinae muscles during all measurements. Paired t-tests, Pearson correlation coefficient, and Wilcoxon's test were used to analyze the data.RESULTS: Difference of mean force values between the devices was statistically significant in all directions. Pearson correlation coefficient varied between 0.73 and 0.89 and it was highest in cervical flexion. EMG activities were significantly different only in the left CES during flexion.DISCUSSION: The helmet-attached gauge is a valid tool for measuring isometric neck muscle strength and is best used as a means to compare individual differences in strength levels or to track the progress of strength development.Nyländen P, Virmavirta M, Sovelius R, Kyröläinen H, Honkanen T. A flight helmet-attached force gauge for measuring isometric neck muscle strength. Aerosp Med Hum Perform. 2023; 94(6):480-484.

A heuristic model-based approach for compensating wind effects in ski jumping.

Wind influences the jump length in ski jumping, which raises questions about the fairness. To counteract the wind problem, the International Ski Federation has introduced a wind compensation system in 2009: time-averaged wind velocity components tangential to the landing slope are obtained from several sites along the landing slope, and these data are used in a linear statistical model for estimating the jump length effect of wind. This is considered in the total score of the ski jump. However, it has been shown that the jump length effect estimates can be inaccurate and misleading. The present article introduces an alternative mathematical wind compensation approach that is based on an accurate mechanistic model of the flight phase. This estimates the jump length effect as difference between the jump length of the real ski jump at the given wind condition and the computed jump length of the simulated ski jump at calm wind. Inputs for the computer simulation are the initial flight velocity and aerodynamic coefficients of the real ski jump that can be obtained from kinematic and wind velocity data collected during the flight. The initial flight velocity is readily available from the kinematic data and inverse dynamics can be used to compute the aerodynamic coefficients. The accuracy of the estimated jump length effect of the mechanistic model-based approach depends only on the measurement errors in the kinematic and wind velocity data, but not on inaccuracies of an approach that is based on a linear statistical model.

Is it still important to be light in ski jumping?

In ski jumping low body weight development resulted in some serious underweight problems and therefore the International Ski Federation (FIS) decided to solve the problem by relating maximum ski length to Body Mass Index (BMI) in 2004. The present study examined the current relationship between body weight, ski length and performance (jumping distance) in ski jumping. By adopting the BMI regulation to specifications for competition equipment, the FIS succeeded in stopping the alarming development of underweight problems in ski jumping. However, as the results of the present study show, the BMI regulation adopted by the FIS has reduced the advantage of being light, but despite the use of shorter skis it is still beneficial to be light within certain limits. The present parametric study suggests that the weight of the jumper is a more sensitive factor to jump length than ski area (ski length). In fact, sensitivity analysis shows that reducing BMI by 1% requires a reduction of approximately 2.0% in ski area to compensate each other. Based on the available information of the complex relationship between body morphology and performance in ski jumping there seems to be no further need for a change in the BMI regulation.

60-Hour Sleep Deprivation Affects Submaximal but Not Maximal Physical Performance.

The effect of 60-h sleep deprivation (SD) on physical performance and motor control was studied. Twenty cadets were measured for aerobic performance (VO2) before and immediately after the SD period. Maximal strength and EMG of the knee extensor muscles were measured before and after 60 h of SD. Balance, reaction times and motor control were assessed every evening and morning during the SD period. Main effects were observed for heart rate (p = 0.002, partial eta squared: 0.669), VO2 (p = 0.004, partial eta squared: 0.621), ventilation (p = 0.016, partial eta squared: 0.049), and lactate concentration (p = 0.022, partial eta squared: 0.501), whereas RER remained unaltered (p = 0.213, partial eta squared: 0.166). Pairwise comparisons revealed decreased values at submaximal loads in heart rate, VO2, ventilation (all p < 0.05) but not in RER, whereas all of their respective maximal values remained unchanged. Moreover, pairwise comparisons revealed decreased lactate concentration at maximal performance but only at 8-min time point during submaximal workloads (p < 0.05). Pairwise comparisons of maximal strength, EMG and rate of force development revealed no change after SD. Main effects were observed for motor and postural control, as well as for reaction times (all p < 0.05), whereas pairwise comparison did not reveal a consistent pattern of change. In conclusion, motor control can mostly be maintained during 60-h SD, and maximal neuromuscular and aerobic performances are unaffected. However, submaximal cardiorespiratory responses seem to be attenuated after SD.

Determining the location of the body׳s center of mass for different groups of physically active people.

The purpose of the present study was to compare the location of the body center of mass (CoM) determined by using a high accuracy reaction board (RB) and two different segment parameter models for motion analysis (Dempster, 1955, DEM and de Leva, 1996 adjusted from Zatsiorsky and Seluyanov, ZAT). The body CoM (expressed as percentage of the total body height) was determined from several subjects including athletes as well as physically active students and sedentary people. Some significant differences were found in the location of the body CoM between the used segment models and the reaction board method for all male subjects (n=58, 57.03±0.79%, 56.20±0.76% and 57.60±0.76% for RB, ZAT and DEM, respectively) and separately for male (n=12, RB 57.02±0.41%, ZAT 56.74±0.62%, DEM 58.19±0.60%) and female (n=12, RB 55.91±0.88%, ZAT 57.24±0.77%) students of physical activity. The ZAT model was a good match with RB for high jumpers (56.26±0.94% and 56.63±0.56%) whereas the DEM model was better for gymnasts (57.38±0.46% and 57.89±0.49%) and throwers (58.19±0.69% and 57.79±0.45%). For ice hockey players (IH) and ski jumpers (SJ) both segment models, ZAT and DEM, differed significantly from the reaction board results. The results of the present study showed that careful attention should be paid while selecting the proper model for motion analysis of different type of athletes.

The effect of wind on jumping distance in ski jumping--fairness assessed.

The special wind compensation system recently adopted by Fédération Internationale de Ski (FIS; International Ski Federation) to consider the effects of changing wind conditions has caused some controversy. Here, the effect of wind on jumping distance in ski jumping was studied by means of computer simulation and compared with the wind compensation factors used by FIS during the World Cup season 2009/2010. The results showed clearly that the effect of increasing head/tail wind on jumping distance is not linear: +17.4 m/-29.1 m, respectively, for a wind speed of 3 m/s. The linear formula used in the trial period of the wind compensation system was found to be appropriate only for a limited range of jumping distances as the gradient of the landing slope slows down the rate of distance change in long jumps.

Effect of weighted vest suit worn during daily activities on running speed, jumping power, and agility in young men.

Previous weighted vest interventions using exercise in addition to hypergravity have been successful in improving postural balance and power production capacity. The purpose of this study was to investigate if hypergravity alone in daily activities excluding sporting activities is effective in improving neuromuscular performance in young adults. Eight male subjects (age = 32 [SD: 6] years, height = 178 [5] cm, and body mass = 81 [8] kg) wore weighted vests 3 d·wk for 3 weeks during waking hours, excluding sporting activities. Control group comprised 9 male subjects (age = 32 [6] years, height = 179 [5] cm, and body mass = 83 [9] kg). Performance was assessed with countermovement jump (body mass normalized peak power), figure-of-8 running test (running time), and running velocity test at baseline and at the end of the intervention. At baseline, the groups did not differ from each other (multivariate analysis of variance [MANOVA] p = 0.828). A significant group × time interaction (MANOVA F = 5.1, p = 0.015) was observed for performance variables. Analysis of covariance indicated that the intervention improved the figure-of-8 running time (p = 0.016) (-2.2 vs. 0.5%), whereas normalized peak power (0.0 vs. 1.6%) and running velocity (1.3 vs. 0.1%) were unaffected (p ≥ 0.095). Wearing weighted vests was effective in slightly improving agility-related performance in young men. Because the effect was small, applying hypergravity only during exercise probably suffices. It appears that a proper volume and intensity of hypergravity could be in the order of 5-10% body weight vest worn during up to 50% of the training sessions for a period of 3-4 weeks.

Ski jumping takeoff in a wind tunnel with skis.

The effect of skis on the force-time characteristics of the simulated ski jumping takeoff was examined in a wind tunnel. Takeoff forces were recorded with a force plate installed under the tunnel floor. Signals from the front and rear parts of the force plate were collected separately to examine the anteroposterior balance of the jumpers during the takeoff. Two ski jumpers performed simulated takeoffs, first without skis in nonwind conditions and in various wind conditions. Thereafter, the same experiments were repeated with skis. The jumpers were able to perform very natural takeoff actions (similar to the actual takeoff) with skis in wind tunnel. According to the subjective feeling of the jumpers, the simulated ski jumping takeoff with skis was even easier to perform than the earlier trials without skis. Skis did not much influence the force levels produced during the takeoff but they still changed the force distribution under the feet. Contribution of the forces produced under the rear part of the feet was emphasized probably because the strong dorsiflexion is needed for lifting the skis to the proper flight position. The results presented in this experiment emphasize that research on ski jumping takeoff can be advanced by using wind tunnels.

Comparison of running kinematics between elite and national-standard 1500-m runners.

The aim of this study was to determine whether elite 1500-m runners differ in their running kinematics from national-standard 1500-m runners. Six national-standard male runners (seasonal best: 3 min 49.2 s +/- 3.2 s) were assessed during the second lap of a 1500-m race. Their running kinematics was then compared with those of five elite runners (seasonal best: 3 min 35.6 s +/- 2.6 s) analysed during the second lap of the men's 1500-m final at the 2005 World Championships. Data were collected using two high-speed cameras operating at 200 Hz with a three-dimensional pan and tilt system. Running speed was the same for both groups. Despite the similar contact times, the minimum knee angle during the stance phase was greater and the average extension velocity of the knee angle in the same phase slower in the elite runners than in the national-standard runners. In addition, the running technique of the elite runners appears to be characterized by a more efficient function of the hip joint. In conclusion, elite runners may utilize elastic energy more effectively, which, in combination with minimum concentric work, leads to improvements in their running performance.

Take-off analysis of the Olympic ski jumping competition (HS-106m).

The take-off phase (approximately 6m) of the jumps of all athletes participating in the individual HS-106m hill ski jumping competition at the Torino Olympics was filmed with two high-speed cameras. The high altitude of the Pragelato ski jumping venue (1600m) and slight tail wind in the final jumping round were expected to affect the results of this competition. The most significant correlation with the length of the jump was found in the in-run velocity (r=0.628, p<0.001, n=50). This was a surprise in Olympic level ski jumping, and suggests that good jumpers simply had smaller friction between their skis and the in-run tracks and/or the aerodynamic quality of their in-run position was better. Angular velocity of the hip joint of the best jumpers was also correlated with jumping distance (r=0.651, p<0.05, n=10). The best jumpers in this competition exhibited very different take-off techniques, but still they jumped approximately the same distance. This certainly improves the interests in ski jumping among athletes and spectators. The comparison between the take-off techniques of the best jumpers showed that even though the more marked upper body movement creates higher air resistance, it does not necessarily result in shorter jumping distance if the exposure time to high air resistance is not too long. A comparison between the first and second round jumps of the same jumpers showed that the final results in this competition were at least partly affected by the wind conditions.

Characteristics of the early flight phase in the Olympic ski jumping competition.

Early flight phase (approximately 40 m) of the athletes participating in the final round of the individual large hill ski jumping competition in Salt Lake City Olympics was filmed with two high-speed pan & tilt video cameras. The results showed that jumpers' steady flight position was almost completed within 0.5s. The most significant correlation with the length of the jump was found in the angle between the skis and body (r=.714, p.001 at 1.1s after the take-off). This particular phase seemed to be important because the ski angle of attack was also related to the jumping distance at the same phase. Although the more upright ski position relative to flight path resulted in longer jumping distance, the winner of the competition had significantly lower ski position as compared to the other good jumpers. This may be due to the high altitude (>2000 m) of the ski jumping stadium in this competition. Because of the low air density, the aerodynamic forces were also low and this probably caused less skillful jumpers to lean too much forward at this phase. Maintenance of speed seemed to be emphasized in this particular competition.