Heart rate and match analysis in pre-pubescent soccer players.

The aim of this study was to compare match analysis (using video recordings) and the physiological load (heart rate measured every 5 s, blood lactate measured after the warm-up, first half and second half) of six 11-year-old soccer players during official games of eleven-a-side on a regular-sized pitch (100 x 65 m) and of seven-a-side on a smaller pitch (60 x 40 m). In both games, heart rate exceeded 170 beats x min(-1) 84% of the time, while blood lactate ranged from 1.4 to 8.1 mmol l(-1). No significant differences were recorded for the physiological parameters. For both matches, walking comprised 38% of total time, running 55%, inactivity 3% and jumping 3%. Although there were no significant differences between halves or matches, running for less than 10 s was 10% more frequent in the seven-a-side game. In the seven-a-side game, there were significantly more passes and significantly fewer tackles, suggesting that seven-a-side matches played on smaller pitches may be more suitable for pre-pubescent soccer players.

Energy cost and energy sources of ball routine in rhythmic gymnasts.

The energy cost and the different energy sources of competitive rhythmic ball-routines were assessed in nine young elite rhythmic gymnasts (13-16 years of age). The overall energy requirement of ball exercise (VO2eq) was obtained by adding the amount of VO2 during exercise above resting (VO2ex) to the VO2 up to the fast component of recovery (VO2al) and to the energy equivalent of peak blood lactate accumulation (VO2la-) of recovery. The lactate (La) curve up to 25 minutes of recovery always showed La peaks at 3 min after exercise (4.0 +/- 0.4 mmol/l) and values still above rest at 25 min (2.3 +/- 0.5 mmol/l). Although ball routines were short in duration (90 s), the metabolic power requirement was 1.1 times higher than the subject's VO2max. The energy cost (VO2eq) amounted to 81 +/- 5 ml x kg(-1). Higher fractions of VO2eq were VO2ex 49% and VO2al 42%, while the remaining 9% was due to VO2la-. The aerobic source resulted in the most utilized system due to the subjects' high VO2max (52.7 ml x kg(-1) x min(-1)) and anaerobic threshold (LT = 84.4%). The HR and the peak lactate values of ball routine were similar to the values recorded at LT step during treadmill test. Although the HR and VO2 values were significantly correlated (during pre-exercise, exercise, and fast recovery), the exercise intensity derived from HR Kanvonen method during ball routine did not correspond to the % of VO2max.

Effects of a low-intensity conditioning programme on VO2max and maximal instantaneous peak power in elderly women.

The effects of 12 weeks of a low-intensity general conditioning programme on maximal instantaneous peak power (Wpeak) and maximal oxygen uptake (VO2max) were examined in 20 elderly women. After medical, familiarisation, and ethical procedures, the subjects were randomly divided into either a training and or a control group. The training group [n = 11; mean (SD) age 63.0 (3.1) years] agreed to take part in a 12-week training programme at an exercise intensity kept under 60% of the heart rate reserve for about 60 min, 3 times a week. The control group [n = 9; mean (SD) age 63.5 (3.3) years] did not perform any particular physical training. Before and after the training period, all participants underwent anthropometric measures and a maximal cycling test to exhaustion to measure their VO2max. In addition, Wpeak was determined 1 week later by the subjects performing a vertical jump from a squatting position on a force platform. Following training, neither the anthropometric characteristics nor the VO2max changed in either of the groups. In contrast, Wpeak increased significantly (P < 0.001) in the training group, but did not change in the control group. This result could be interpreted as the result of an improved level of neuromuscular activation. Furthermore, it shows that although muscle power declines with age at a faster rate than does aerobic power, its sensitivity to training seems to be higher than that of the aerobic system.

Reliability of isokinetic knee extension and flexion strength testing in elderly women.

BACKGROUND: Intertrial and test-retest reliability of isokinetic knee extension and flexion strength measurements was studied in eighteen elderly women (mean age 68 +/- 5 yrs), using increasing and decreasing angular velocity testing procedures. EXPERIMENTAL DESIGN: five reciprocal knee extensions and flexions at three different angular velocities (90, 120, and 180 deg/sec) were performed by means of a MERAC apparatus on two occasions fifteen days apart. MEASURES: Data relative to torque, power and work were considered. RESULTS: Statistically significant differences were found often among the five trials and intraclass correlation coefficients, ranging from 0.03 to 0.90 for extensor muscles; ranging from 0.44 to 0.89 for flexor muscles, were shown among the best three outputs. Peak values were reached within the first three repetitions, though a 20% chance to produce peak outputs was shown in the last two repetitions. Increasing and decreasing test velocity procedures did not consistently show statistically significance for peak outputs. Generally, for each isokinetic parameter higher and more frequently significant correlation coefficients between test and retest experimental sessions were found for peak values (ranging from 0.36 to 0.80) with respect to mean values (ranging from 0.22 to 0.74). CONCLUSIONS: These data suggest that a test procedure including five trials tends to increase the chance of producing the best peak outputs. Furthermore, considering the best peak and mean performances could be more appropriate when studying elderly women.

Determinants of maximal instantaneous muscle power in women aged 50-75 years.

The present study aimed at analysing the age-related decline in maximal muscle power (W) in 52 sedentary healthy women aged between 50 and 75 years to determine whether force or velocity is the major determinant. Maximal muscle power was estimated from two types of vertical jumps, squatting (SJ) and countermovement (CmJ), performed on a force platform. It was obtained by measuring the vertical force (F(opt)) applied to the body centre of gravity and calculating the corresponding vertical velocity (v(opt)). An age-related decline in absolute W was statistically significant in all the conditions examined and in both peak W and average power (W) values. The decrease in v(opt) was also statistically significant. Also F(opt) declined but this reduction was not statistically significant with the exception of the average value in CmJ. Not surprisingly the highest W were obtained in CmJ, and the difference in power production between the two types of jump showed an age-related decrement only in W. The main finding of the study was the demonstration that v(opt) was the critical determinant of the age-related decline in W in healthy elderly women.

Low intensity physical training in older subjects.

BACKGROUND: This study was designed to evaluate the effects of a low intensity general training program (< 50% of heart rate reserve) on physical fitness of healthy older subjects, by comparing maximal and submaximal indices of training response. METHODS: Twenty-two volunteers over 60 years of age participated in the present study. The sample was randomly divided in an experimental group of 13 older subjects (3 men and 10 women, mean age 63.5 +/- 3 years) while the remaining 9 subjects (3 men and 6 women, mean age 64.2 +/- 4 years) served as inactive control group. After medical screening all participants were evaluated before and after 12 weeks in which the experimental subjects underwent a low intensity training. Each subjects-either inactive or active-performed two treadmill tests at two-days interval, to measure maximal and submaximal responses to exercise, respectively. Heart rate (HR), oxygen uptake (VO2) and pulmonary ventilation (VE) were measured using a telemetric apparatus. RESULTS: The major finding of the study was the significant improvement in submaximal response to exercise of experimental subjects, expressed by the reduction in HR, VO2 VE while VO2 max did not change. CONCLUSIONS: Thus, it appears that a low intensity general training similar to that followed in the present study may represent a good means to improve physical fitness in healthy elderly people. Similarly, this study supports the effectiveness of evaluation tests based on submaximal responses to exercise in this population.

EMG patterns during running: Intra- and inter-individual variability.

Rectified surface electromyographic (EMG) patterns of five healthy, young, physically-fit subjects running at 4.2 m s(-1) on a treadmill were recorded with the objective of defining a normal profile of EMG activity for running gait. This knowledge is important in understanding how the central nervous system (CNS) controls simple running tasks under normal conditions. The EMG signals from seven muscles (erector spinae, rectus femoris, vastus medialis, vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius) were recorded, together with footswitch signals. The intra- and inter-individual variability of each muscle's EMG profile and peak times were analysed. Interindividual EMG peak time values were analysed to define the timing of the activity of the muscles studied relative to the stride cycle and its subphases. For each muscle, little variation was found within individuals in EMG profile and peak time across trials, but differences between subjects were significant (P < 0.01). EMG peak time analysis showed two distinct activation sequences of different muscles: the first at stance phase and the second at terminal swing. In conclusion, in spite of a significant variability among subjects in EMG profile and peak time values for each muscle, the EMG peak timing analysis showed a sequence of activation at stance phase, no EMG peak activity during the first double swing and another sequence of activation during terminal swing. These findings are evidence of a neuromuscular control strategy common to all subjects.

Decrease of endurance performance during Olympic Triathlon.

The present study was carried out in order to quantify the athlete's endurance impairment after two out of three sequential events of Olympic Triathlon (OT). Furthermore the significance of ventilatory threshold (Tvent) and peak of oxygen uptake (VO2peak) as triathlete's performance predictors was assessed. Tvent and VO2peak were measured in six male triathletes performing an incremental treadmill test a week before an ad hoc triathlon event. The same test was applied immediately after the first two segments of the triathlon (1.5 km swim, 32 km bike). VO2peak and Tvent measured during the latter test were reduced compared to the first test. VO2peak decreased from 69 to 64 ml.kg-1.min-1 and Tvent from 58 to 51 ml.kg-1.min-1 p < 0.01), respectively. VO2peak and Tvent measured in the first test were well correlated (P < 0.05) to both running and cycling times. The Tvent measured during the second test was related to the running time but with a higher significance (p < 0.01) than in the first test. The impairment in the endurance performance induced by the first two segments of OT is an important aspect to consider both in training and in race strategy. These results also provide evidence that VO2peak and Tvent are good predictors of triathlon performance at least in cycling and running events.

Heart rate, alveolar gases and blood lactate during synchronized swimming.

Heart rate, alveolar gas partial pressures and blood lactate (BLa) concentration were measured during synchronized swimming in six subjects. During upside-down breath-holding lasting 50 s, heart rate fell progressively from 98 +/- 14 to 70 +/- 7 beats min-1 (mean +/- S.D.). While breath-holding during the compulsory figures, the subjects' heart rate increased to 142 +/- 5 beats min-1 and then fell to 72 +/- 10 beats min-1. At the end of breath-holding, alveolar oxygen pressure had fallen significantly (60 mmHg), whereas alveolar carbon dioxide pressure showed only minor changes (48 mmHg). The increase in BLa concentration due to the execution of compulsory figures was approximately 1 mM; in the free routines, BLa concentration increased by 3.4 +/- 0.5 mM. The net energy cost of completing a compulsory figures lasting 45 s was 34.6 kJ.

Force and power of preferred and non-preferred leg in young soccer players.

The purpose of this study was to assess the effects of soccer training on strength and power of leg extensor muscles in preadolescent boys and their possible influence in developing a muscular lateral dominance. Twenty male children (mean age 9.6 yr), ten soccer players and ten untrained subjects, participated in this study. Force and power were measured at five constant cranking velocities on an isokinetic bicycle dinamometer. Each isokinetic load was given after each trial. Force and power outputs were calculated for each limb. Soccer players always showed higher and statistically significant differences (p < 0.05) for force and power values for all considered pedal frequencies. No significant differences were observed for force and power values between preferred and non preferred limb. The results demonstrate the effect of soccer training on the increase of force and power of both legs regardless of lateral dominance.

Prediction of ramp traversability for wheelchair dependent individuals.

The purpose of this research was to obtain a single objective criterion that would constitute a reliable prediction of length and grade limits for ramps that can be traversed by any special category of wheelchair dependent individuals (WDI). The maximal voluntary force (MVC) is the main limiting factor of the performance of WDI, thus the force required to traverse a ramp has been established by means of a simple mechanical model. The real time course of force application during ascent was experimentally obtained. Then, a simplified law of force application was introduced in a computer simulation program of kinetics and kinematics of ascent. Inputs to the model were also the mass of the subject plus wheelchair, the initial velocity of the chair, and the ramp length. The output of the program was the force requirement for any given length/grade. When capsizing conditions were encountered the simulation ended. We tested the results thus obtained having some selected WDI successfully traversing ramps with the predicted length/grade specifications.

Assessment of static balance in children.

The ability in maintaining body balance of 6-, 8-, and 10-year-old children performing three balance tests on a force platform was studied. Thirty adult subjects served as a reference group. The mean radius (MR) of the posturogram and the mean speed (MS) of the center of foot pressure (COP) were used as the measuring parameters. Data were analyzed using two-way ANOVA, the Sheffe test and the Student "t" test with a .05 level of significance. A decrease with age in both mean radius and mean speed, indicating an increase in balance ability, was noted. A significant age main effect was found on all tests while significant gender main effect occurred only on the Tandem test. No significant age/sex interaction was found. Significant differences between the 10-year-old and adult groups occurred only in the more difficult balance tests.

Lumbar spine loading during half-squat exercises.

Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.

Angular displacements in the upper body of AK amputees during level walking.

The angular displacements of the longitudinal axis of the trunk, and of the latero-lateral axes of pelvis and shoulder girdle were measured in five normal subjects and four AK amputees during level walking at different speeds. Amputees used single axis prostheses with the SACH foot. Spatial measurements were carried out in three dimensions by means of a photogrammetric technique. The time functions of the target angles underwent harmonic analysis. Based on the Fourier coefficients, comparison was made between normal subjects' and amputees' angular displacements. Relevant findings permitted the identification of compensatory mechanisms adopted by amputees at trunk level as well as the assessment of the relationship between these latter mechanisms and those put into action at lower limb level.

Biomechanics of sit-up exercises.

Sit-up exercises performed by four male subjects revealed the presence of initial lumbar "hollowing" (lumbar curvature), or trunk hyperextension, or both prior to trunk flexion. Maximum muscular moment developed at the hip joint, which varied with sit-up exercise, was of moderate order of magnitude. Intraesophageal pressure, cardiopulmonary response, and metabolic response to a commonly used sit-up exercise (curl-up) reveals it to be a light exercise which stresses the muscles of the lower limbs as well as those of the trunk, especially the abdominal muscle group.