The application of principal component analysis to quantify technique in sports.

Analyzing an athlete's "technique," sport scientists often focus on preselected variables that quantify important aspects of movement. In contrast, coaches and practitioners typically describe movements in terms of basic postures and movement components using subjective and qualitative features. A challenge for sport scientists is finding an appropriate quantitative methodology that incorporates the holistic perspective of human observers. Using alpine ski racing as an example, this study explores principal component analysis (PCA) as a mathematical method to decompose a complex movement pattern into its main movement components. Ski racing movements were recorded by determining the three-dimensional coordinates of 26 points on each skier which were subsequently interpreted as a 78-dimensional posture vector at each time point. PCA was then used to determine the mean posture and principal movements (PMk ) carried out by the athletes. The first four PMk contained 95.5 ± 0.5% of the variance in the posture vectors which quantified changes in body inclination, vertical or fore-aft movement of the trunk, and distance between skis. In summary, calculating PMk offered a data-driven, quantitative, and objective method of analyzing human movement that is similar to how human observers such as coaches or ski instructors would describe the movement.

A systematic video analysis of 69 injury cases in World Cup alpine skiing.

We have limited insight into how injuries occur in professional ski racing. The aim of this study was to describe the injury situations in World Cup alpine skiing. Injuries reported through the International Ski Federation Injury Surveillance System for three consecutive World Cup seasons (2006-2009) were obtained on video. In total, 69 injuries and 124 runs of matched controls were analysed by five experts to evaluate the skiing situation, skier behavior, as well as piste-related factors. A chi-square test (95% CI, P ≤ 0.05) was used to examine whether there was a difference between course sections regarding where the injury situation occurred. The skier was most frequently turning (n = 55) or landing from a jump (n = 13) at the time of injury. Most of the injuries to the head and upper body (96%) resulted from crashes, while the majority of knee injuries (83%) occurred while the skier was still skiing. Gate contact contributed to 30% of the injuries, while 9% occurred at contact with safety nets/material. Almost half of the injuries (46%) occurred in the final fourth of the course. A particular concern was the high contribution of inappropriate gate contact and the high-energy impacts to the body when crashing.

Presence of acyl-homoserine lactones in 57 members of the Vibrionaceae family.

AIMS: The aim of this study was to use a sensitive method to screen and quantify 57 Vibrionaceae strains for the production of acyl-homoserine lactones (AHLs) and map the resulting AHL profiles onto a host phylogeny. METHODS AND RESULTS: We used a high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) protocol to measure AHLs in spent media after bacterial growth. First, the presence/absence of AHLs (qualitative analysis) was measured to choose internal standard for subsequent quantitative AHL measurements. We screened 57 strains from three genera (Aliivibrio, Photobacterium and Vibrio) of the same family (i.e. Vibrionaceae). Our results show that about half of the isolates produced multiple AHLs, typically at 25-5000 nmol l(-1) . CONCLUSIONS: This work shows that production of AHL quorum sensing signals is found widespread among Vibrionaceae bacteria and that closely related strains typically produce similar AHL profiles. SIGNIFICANCE AND IMPACT OF THE STUDY: The AHL detection protocol presented in this study can be applied to a broad range of bacterial samples and may contribute to a wider mapping of AHL production in bacteria, for example, in clinically relevant strains.

Recognition of the A chain carboxy-terminal heparin binding region of fibronectin involves multiple sites: two contiguous sequences act independently to promote neural cell adhesion.

Cellular interactions with fibronectin-treated substrata have a complex molecular basis involving multiple domains. A carboxy-terminal cell and heparin binding region of fibronectin (FN) is particularly interesting because it is a strong promoter of neurite outgrowth (Rogers, S.L., J.B. McCarthy, S.L. Palm, L.T. Furcht, and P.C. Letourneau, 1985. J. Neurosci. 5:369-378) and cell attachment (McCarthy, J.B., S.T. Hagen, and L.T. Furcht. 1986. J. Cell Biol. 102:179-188). To further understand the molecular mechanisms of neuronal interactions with this region of FN, we screened two peptides from the 33-kD heparin binding fragment of the FN A chain, FN-C/H II (KNNQKSEPLIGRKKT) and CS1 (Humphries, M.J., A. Komoriya, S.K. Akiyama, K. Olden, and K.M. Yamada. 1987. J. Biol. Chem. 262:6886-6892), for their ability to promote B104 neuroblastoma cell-substratum adhesion and neurite outgrowth. Both FN-C/H II and CS1 promoted B104 cell attachment in a concentration-dependent and saturable manner, with attachment to FN-C/H II exceeding attachment to CS1. In solution, both exogenous FN-C/H II or CS1 partially inhibited cell adhesion to the 33-kD fragment. Similar results were obtained with anti-FN-C/H II antibodies. In contrast, soluble GRGDSP did not affect B104 cell adhesion to FN-C/H II. These results indicate that both FN-C/H II and CS1 represent distinct, RGD-independent, cell adhesion-promoting sites active within the 33-kD fragment, and further define FN-C/H II as a novel neural recognition sequence in FN. B104 adhesion to FN-C/H II and CS1 differs in sensitivity to heparin, yet each peptide inhibited adhesion to the other peptide, suggesting cell adhesion is somehow related at the cellular level. Within the A chain 33-kD fragment, FN-C/H II and CS1 are contiguous, and might represent components of a larger domain with greater neurite-promoting activity since only the 33-kD fragment, and neither individual peptide, was effective at promoting B104 neurite outgrowth. These data further support the hypothesis that cell responses to FN are mediated by multiple sites involving both heparin-sensitive and -insensitive mechanisms.

Sarcomere lengthening and tension drop in the latent period of isolated frog skeletal muscle fibers.

A laser diffraction technique has been developed for registering small changes in sarcomere length. The technique is capable of resolving changes as small as 0.2 A in isolated frog skeletal muscle fibers. The small sarcomere lengthening that accompanies the drop in tension in the latent period of contraction was investigated. We suggest this lengthening be named latency elongation (LE). The LE is present in a completely slack fiber and must, therefore, be caused by a forcible lengthening process. Furthermore, the LE is dependent on the existence of an overlap between thin and tick filaments. The rate of elongation and the time interval between stimulation and maximum elongation may vary along the fiber. The maximum elongation was 3-5 A per sarcomere. At any instant the drop in tension is a product of the sum of sarcomere lengthenings along the fiber and the slope stiffness of the series elasticity. The latency relaxation (LR) could be registered in the sarcomere length range from 2.2 mum to 3.6-3.7 mum. The amplitude went through a sharp maximum at 3.0-3.1 mum. In the sarcomere length range from 2.2 to 2.8 mum the delay from onset to maximum LR was nearly proportional to the distance from the Z-line to the overlap zone. A working hypothesis is presented. It is suggested that the LE is caused by a lengthening of the thin filaments.

The stiffness under isotonic releases during a twitch of a frog muscle fibre.

These investigations were undertaken to elucidate whether the difference between the time courses of the isometric tension and the velocity of shortening upon releases to a given isotonic load various times during a twitch is due to a change in the kinetics of the individual cross-bridges, i.e. in the rate constants governing the transitions between the various strongly bound cross-bridge states. Single skeletal muscle fibres from the frog (Rana temporaria, sarcomere length 2.3 microns, temperature 4-6 degrees C) were stimulated to produce isometric twitches and released after various delays to shorten isotonically against finite loads (P). Force, stiffness (K, measured by longitudinal oscillation 0.3-0.8 nm per half-sarcomere peak-to-peak, 2 kHz), and change in length were measured simultaneously. The velocity of shortening (V) was estimated as the quasi steady-state value, i.e. the value attained after the initial oscillatory transient response to the change in length preceding the isotonic shortening. A reduction in P led to a reduction in K, however, the relative reduction in K was not as great as the relative reduction in P. Thus, when extrapolated to P = O, K was about one third of its peak isometric value. Under the assumption that K is to the first order of approximation proportional to the number of strongly bound cross-bridges, P was divided by K to give an estimate of the average load per cross-bridge yo = P/K.V showed an almost linear dependence on yo (correlation coefficients 0.95-0.998). The slope and intercept of this relation (regression analysis) showed no dependence on the delay after stimulation of the release to the isotonic load. The results can be explained if the kinetic properties of the individual strongly bound cross-bridges are unaffected by the level of activation which changes during the course of the contraction.

Calcium transients in skeletal muscle fibres under isometric conditions and during and after a quick stretch.

The transient change in the sarcoplasmic concentration of Ca2+ was measured in intact fibres isolated from the anterior tibial muscle of the frog Litoria moorei. The fibres had been injected with the calcium-sensitive dye arsenazo III and the change of the calcium concentration was calculated from the changes in light absorbance at 570, 600 and 720 nm wavelengths. Absorbance and force were measured under three different conditions: (1) during a normal isometric twitch, (2) when a quick ramp-and-hold stretch had been applied to the fibre during onset of the contraction, and (3) when the fibre was allowed to contract isometrically at a length corresponding to the final length of the stretch. A method was devised to neutralize most of the movement artefacts encountered in such measurements. While the quick stretch caused substantial increase in the level and the duration of the contractile force such as originally described in whole muscle by A. V. Hill, the calcium transients appeared basically unaffected. It thus seems that the mechanism behind the phenomenon of the force enhancement lies at a step in the excitation-contraction coupling subsequent to the calcium release. From the present results, however, it is not clear whether the phenomenon is caused by an increase in the level of activation of the calcium-dependent regulatory system, or whether it is to be found in the acto-myosin interaction itself. The latter alternative would be consistent with the stiffness measurements published earlier.

The dependence of the latency relaxation on temperature in single muscle fibres of the frog.

The time course of the latency relaxation was studied at various temperatures in the range 0-26 degrees. Over the entire range the time of onset of the drop in tension, t1, was independent of sarcomere length. At temperatures above 12-15 degrees C the falling phase had a point of inflexion, while at lower temperatures there was an interval during which the tension fell at a constant rate. The time when the rate of drop in tension had passed its maximum value tL2, the time to the maximum drop in tension t2, and the time when the tension crossed the resting level t3, all showed linear dependence on sarcomere length in the range from 2.1 to 2.7-3.4 microgram. In this range the durations of the intervals tL2-t1, t2-t1, and t3-t1 were nearly proportional to the distance from the Z-line to the end of the zone of overlap between the thick and the thin filaments. This could be explained as the activation being a longitudinal process starting from the Z-line. The slopes (dt/dS) of the linear portions of the time variables t1.2, t2, and t3 in a time-sarcomere length (S) diagram all had the same dependence on temperature giving a Q10 of 1.75. Under the assumption that the activation process followed a diffusion of calcium from the Z-line region to the zone of overlap a diffusion coefficient was estimated. At room temperature it had a magnitude of about 1/20 of that for calcium chloride in water. It had a dependence on temperature corresponding to an Arrhenius activation energy of about 37 kJ/mol which is about twice the activation energy for a simple diffusion of calcium in water. The results can be interpreted in terms of the time course of the latency relaxation mainly reflecting a longitudinal diffusion of calcium ions in the sarcoplasm.

Increase of resistance to stretch during the latent period in single muscle fibres of the frog.

The time from stimulation to the first change of the extensibility in an isolated skeletal muscle fibre was measured by subjecting the fibre to a rapid, small stretch at various times during the latent period. The experiments were performed at constant temperatures in the range 1-16 degrees C. Irrespective of the temperature, the first increase of the resistance to stretch occurred after the onset of the latency relaxation. At a temperature or 10 degrees C and a sarcomere length of 3 microgram the resistance started to increase 5.5 ms after stimulation, i.e. 1.5-2 ms after the onset of the drop in tension, and then increased nearly linearly with time. Corresponding to the end of the latent period, i.e. when the tension recrosses the resting level, the amplitude of the response was about 1.5 times its resting value. There was an interval between the onset of increase f the resistance to stretch and the time when the rate of drop in tension had passed its maximum value. The results are compatible with the hypothesis that the latency relaxation arises from a minute lengthening of the thin filaments as proposed by Haugen & Sten-Knudsen, and that attachment and generation of force take place at separate steps of the cross-bridge cycle.

Short-range elasticity after tetanic stimulation in single muscle fibres of the frog.

The time course of the stiffness during the relaxation period following tetanic stimulation was studied in isolated single muscle fibres of the frog. The stiffness was measured by subjecting the fibres to a sudden stretch at constant velocity from an initial sarcomere length of 2.2 microns, and related to the tension carried by the muscle fibre immediately before the stretch. Both stiffness and tension fell close to the resting level during the first second (4 degrees C) after the end of stimulation. While stiffness and tension fell proportionally during the phase of almost exponential decline in tension following the shoulder in the tension recording, the relative drop in stiffness was less than the relative drop in tension during the preceding phase of almost linear decline in tension corresponding to the first 300-400 ms after the end of stimulation.

Changes in contractile dynamics during the course of a twitch of a frog muscle fibre.

Single skeletal muscle fibres from the frog were stimulated to produce isometric twitches and released after a delay to shorten isotonically unloaded or against a finite load (P). When varying the delay, the velocity of the initial shortening (V) against a given non-zero load reached its maximum value earlier than the peak of the isometric tension. The velocity of unloaded shortening (V0, slack test, range: 3.7-5.6 nm ms-1 per half-sarcomere) was independent of the delay of the release. For any given delay, V was hyperbolically related to P, except for the high-load end of the P-V curve at which the velocity took lower values than extrapolated from the hyperbolic relation. The relation between V and the load in units of P1 (corresponding to V = 1 nm ms-1 per half-sarcomere) coincided in the hyperbolic range with the relations obtained at other delays of the release. P1 was basically proportional to the maximum power which also had its peak value during the rising phase of the twitch. The quick releases required to reach the non-hyperbolic range of the P-V curves were estimated to be less than 9 nm per half-sarcomere irrespective of the delay of the release. At load levels in the non-hyperbolic range V could be increased if the quick release was followed by a brief (2 ms) extra reduction in the load preceding the shortening at isotonic load. The results can be explained if the kinetic properties of the individual strongly bound crossbridges are unaffected by the changing level of activation during the course of the contraction. The time-dependence of the non-hyperbolic range of the P-V relation can be accounted for if crossbridges attached before the release remain attached after the release thus constituting an internal load. The difference in time course of isometric tension as compared to velocity of initial shortening against a given load, P1, and maximum power may arise as the result of a reduction in the level of activation caused by the release to the isotonic load level.

The dependence of the short-range elasticity on sarcomere length in resting isolated frog muscle fibres.

The tension response of a resting muscle fibre to a sudden small stretch (ca. 1% of the fibre length) at constant velocity was analyzed according to a mechanical model in which two components are arranged in parallel: (i) The parallel elastic component (PEC) which is responsible for the resting tension of the fibre. (ii) The short-range elastic component (SREC) which has a highly non-linear tension response: Initially, the tension increases linearly with stretch, but with further stretch the increase in tension subsides and a steady tension level is attained. Both the initial short-range elastic stiffness and the steady state tension level increased with increasing sarcomere length up to 2.9-3.3 micrometer where both variables reached maximum values. The maximum value of the steady tension level was about 1% of the maximum twitch tension. With further increase of sarcomere length both the short-range elastic stiffness and the steady tension level decreased and approached zero at a sarcomere length of about 3.7 micrometer. The structural basis for the SREC is considered to be myosin heads which are cross-linking the thick and the thin filaments even in the resting state of the fibre.

The effect of a small stretch on the latency relaxation and the short-range elastic stiffness in isolated frog muscle fibres.

The amplitude of the latency relaxation and the stiffness of the short-range elastic component (SREC) were determined in single muscle fibres before and immediately after subjecting the fibre to a sudden small stretch at constant velocity. After the stretch the amplitude of the latency relaxation was reduced compared to the value obtained before the stretch provided that the velocity of stretch exceeded about 1 mm . ms-1 per half-sarcomere and that the amplitude of the stretch was sufficient to reach the stationary response of the SREC. The effect of the stretch on the amplitude of the latency relaxation subsided after about 4 ms. A reduction of the amplitude of the latency relaxation was accompanied by a reduction of the short-range elastic stiffness. This result is discussed in terms of the various hypotheses put forward to account for the generation of the latency relaxation.

Interleukin-2 enhances chick and rat sympathetic, but not sensory, neurite outgrowth.

Interactions between the immune and nervous systems could be important for normal development and function of both. To determine if a lymphokine, interleukin-2 (IL-2), represents a link between these two systems, sympathetic and sensory neurons from embryonic chick and neonatal rat were cultured in media containing human recombinant IL-2. In chick sympathetic chain and rat superior cervical ganglia cultures, IL-2 enhanced the number of neurons with neurites and the length of those neurites significantly over control cultures. Sensory neurons from chick and rat dorsal root ganglia were not affected by culture in IL-2. Sympathetic neuron response to IL-2 was concentration-dependent, with an optimum around 2-0.2 U/ml (100-10 pM). Immunofluorescence with an anti-IL-2 receptor antibody demonstrated specific staining of sympathetic neurons, but not sensory neurons, implying that sympathetic neurons may have a receptor for IL-2 on their surface.

The time course of the contractile force measured during a twitch under fixed sarcomere length.

A sarcomere length-controlled feedback system was constructed utilizing the laser diffraction technique of Haugen & Sten-Knudsen (1976) to detect sarcomere length changes. The system allowed the sarcomere length to be kept constant within 0.02% during an isometric twitch. The contractile force developed approximates closely to the force exerted by the crossbridges when their translatory movements are prevented. Thus, the force developed under this condition should correspond to the intensity of the active state as defined by A. V. Hill (1949). The time course of the twitch under constant sarcomere length differs substantially from that of the active state curves obtained using quick stretches and quick releases. Thus, the force does not rise quickly to its maximum but rather resembles the fixed-end twitch curve by leading it only slightly (5 ms at 5 degrees C). Its peak value does not reach the level of the tetanic plateau, but is only 9% higher than the maximum fixed-end twitch tension. The force remains above the curve of the fixed-end twitch during its entire course. It is shown that the quick-stretch procedure which results in active state curves as those obtained by A.V. Hill (1949) led to a considerable elongation of the sarcomeres. It is concluded that the slow rise of the contractile force under ordinary isometric conditions is due to properties inherent in the contractile machinery other than those resulting from the extension of series elastic components.

[Six years of experiences from a department of geriatric psychiatry]. / Erfaringer fra en alderspsykiatrisk avdeling gjennom seks år.

After a project period from 1994 to 1997, all hospital-based psychogeriatric services in the Norwegian county of Telemark have been located to one department in the central hospital. The department has three differentiated bed units and one out-patient unit. This article describes the psychogeriatric department before and after the project, and includes an evaluation of the quality of service. The changes following the reorganization have been evaluated with an internal analysis, questionnaires to primary health care personnel and an examination of medical and psychiatric records. In 1995 and 1997, questionnaires were sent to general practitioners and district nurses in Telemark County. An independent consultant examined 40 medical and psychiatric records in 1995 and 1997, evaluating them according to selected quality standards. The response rates among doctors were 59% in 1995 and 48% in 1997. The responses show that primary health care doctors and nurses make use of the department's services and that they are increasingly satisfied with the quality of these services. The examination of medical and psychiatric records shows insufficient documentation of psychiatric symptoms and activities of daily life in 1995, but significant improvements by 1997. There are drawbacks to the evaluation method employed. However, we find it warranted to conclude that the reorganization has been functional and that the quality of services has improved.