Plantar loading in the youth soccer player during common soccer movements and risk for foot injury.

INTRODUCTION: Soccer players are at high risk of stress injuries in the foot. While most research addresses this issue in professional athletes, there is little information concerning young athletes. As soccer is practiced around the world since early infancy, we set out to determine whether young soccer athletes are susceptible to increased foot loading that increase risk factors for foot injuries in a similar manner as reported by the literature to the adult athlete. METHODS: twenty-six male adolescents (mean age 16 years old) were organized into two groups: soccer players (n = 13) and controls (n = 13). Groups were compared regarding foot sensitivity, ankle range of motion, Q-angle, and plantar pressure determined during running and cutting movements performed at maximal speed and using different shoes. RESULTS: Foot sensitivity, ankle range of motion and Q-angle did not differ between the groups. During performance of soccer actions, young players showed higher peak pressure in the lateral region of the foot including the fifth metatarsal region. These higher peaks were minimized by manipulation of the footwear. CONCLUSION: In summary, young soccer athletes show dynamic plantar pressure patterns that are related to foot injury in the adult athlete, and this condition can be minimized by the manipulation of the footwear. Additional attention should be paid to the young athlete in soccer aiming to minimize long-term risk for stress injuries in the foot.

Key determinants of time to 5†m in different ventral swimming start techniques.

The aim of this study was to determine the biomechanical parameters that explain ventral start performance in swimming. For this purpose, 13 elite swimmers performed different variants of the ventral start technique. Two-dimensional video analyses of the aerial and underwater phases were used to assess 16 kinematic parameters from the starting signal to 5 m, and an instrumented starting block was used to assess kinetic data. A Lasso regression was used to reduce the number of parameters, providing the main determinants to starting performance, revealing different combinations of key determinants, depending on the variant (r² ≥ 0.90), with flight distance being the most relevant to all variants (r ≤ -0.80; p < .001). Also, special attention should be given to the total horizontal impulse in the grab start (r = -0.79; p < .001) and to the back foot action in the track and kick starts (r ≤ 0.61; p < .001). In addition, we provide two equations that could be easily used to predict starting performance by assessing block time and flight time (r² = 0.66) or block time and flight distance (r² = 0.83). These data provide relevant contributions to the further understanding of the biomechanics of swimming starts as well as insights for performance analysis and targeted interventions to improve athlete performance.

Validity of a portable force platform for assessing biomechanical parameters in three different tasks.

The aim of this study was to determine the precision and accuracy of the vertical and anterior-posterior force components of the portable PASCO PS-2142 force plate. Impulse, peak force, and time to peak force were assessed and compared to a gold standard force plate in three different tasks: vertical jump, forward jump, and sprint start. Two healthy male participants performed ten trials for each task, resulting in 60 trials. Data analyses revealed good precision and accuracy for the vertical component of the portable force plate, with relative bias and root mean square (RMS) error values nearly the same in all tasks for the impulse, time to peak force, and peak force parameters. Precision and accuracy of the anterior-posterior component were lower for the impulse and time to peak force, with relative bias and RMS error values nearly the same between tasks. Despite the lower precision and accuracy of the anterior-posterior component of the portable force plate, these errors were systematic, reflecting a good repeatability of the measure. In addition, all variables presented good agreement between the portable and gold standard platforms. Our results provide a good perspective for using the aforementioned portable force plate in sports and clinical biomechanics.

Effects of strengthening and stretching exercise programmes on kinematics and kinetics of running in older adults: a randomised controlled trial.

The aim of this study was to investigate the effects of strengthening and stretching exercises on running kinematics and kinetics in older runners. One hundred and five runners (55-75 years) were randomly assigned to either a strengthening (n = 36), flexibility (n = 34) or control (n = 35) group. Running kinematics and kinetics were obtained using an eight-camera system and an instrumented treadmill before and after the eight-week exercise protocol. Measures of strength and flexibility were also obtained using a dynamometer and inclinometer/goniometer. A time effect was observed for the excursion angles of the ankle sagittal (P = 0.004, d = 0.17) and thorax/pelvis transverse (P < 0.001, d = 0.20) plane. Similarly, a time effect was observed for knee transverse plane impulse (P = 0.013, d = 0.26) and ground reaction force propulsion (P = 0.042, d = -0.15). A time effect for hip adduction (P = 0.006, d = 0.69), ankle dorsiflexion (P = 0.002, d = 0.47) and hip internal rotation (P = 0.048, d = 0.30) flexibility, and hip extensor (P = 0.001, d = -0.48) and ankle plantar flexor (P = 0.01, d = 0.39) strength were also observed. However, these changes were irrespective of exercise group. The results of the present study indicate that an eight-week stretching or strengthening protocol, compared to controls, was not effective in altering age-related running biomechanics despite changes in ankle and trunk kinematics, knee kinetics and ground reaction forces along with alterations in muscle strength and flexibility were observed over time.

Effects of changing speed on knee and ankle joint load during walking and running.

Joint moments can be used as an indicator of joint loading and have potential application for sports performance and injury prevention. The effects of changing walking and running speeds on joint moments for the different planes of motion still are debatable. Here, we compared knee and ankle moments during walking and running at different speeds. Data were collected from 11 recreational male runners to determine knee and ankle joint moments during different conditions. Conditions include walking at a comfortable speed (self-selected pacing), fast walking (fastest speed possible), slow running (speed corresponding to 30% slower than running) and running (at 4 m · s(-1) ± 10%). A different joint moment pattern was observed between walking and running. We observed a general increase in joint load for sagittal and frontal planes as speed increased, while the effects of speed were not clear in the transverse plane moments. Although differences tend to be more pronounced when gait changed from walking to running, the peak moments, in general, increased when speed increased from comfortable walking to fast walking and from slow running to running mainly in the sagittal and frontal planes. Knee flexion moment was higher in walking than in running due to larger knee extension. Results suggest caution when recommending walking over running in an attempt to reduce knee joint loading. The different effects of speed increments during walking and running should be considered with regard to the prevention of injuries and for rehabilitation purposes.

Postural sway following cryotherapy in healthy adults.

In light of the wide use of cryotherapy and its potential negative effects on postural stability, little is known about how postural sway is affected, particularly when the whole lower limb is immersed. The purpose of this study was to analyze the influence of cryotherapy on postural sway in healthy males. Twenty-six subjects were randomly assigned into two intervention groups: control (tepid water at ∼26°C) or ice (cold water at ∼11°C). Postural sway was measured through the center of pressure (COP) position while they stood on a force plate during bipedal (70 s) and unipedal (40 s) conditions before and after the subjects were immersed in a water tub up to the umbilical level for 20 min. COP standard deviation (SD) and COP velocity were analyzed in the anterior-posterior (AP) and medial-lateral (ML) directions. Statistical analysis showed that in the bipedal condition cryotherapy increased the COP SD and COP velocity in the ML direction. During the unipedal condition, a higher COP velocity in the AP and ML directions was also reported. Our findings indicate that cryotherapy by immersing the whole lower limb should be used with caution before engaging in challenging postural control activities.

Effects of a noncircular chainring system on muscle activation during cycling.

Previous studies evaluated cycling with noncircular chainrings and suggested that changes in muscle activation would occur in response to altered pedaling mechanics throughout the crank arm revolution. However, no previous study addressed this question. The aim of this study was to compare the magnitude of muscular activity between a conventional and a noncircular crank system during an incremental maximal cycling test. Seven mountain-bike trained cyclists completed two incremental maximal tests, separated by 48 h, one for each crank system. Each test started with a workload of 100 W and was increased by 30 W every minute until exhaustion. Power output, pedaling cadence and heart rate were monitored and compared between the crank systems using paired t-tests. Surface EMG was recorded from the right rectus femoris, vastus medialis, biceps femoris and gastrocnemius medialis. EMG was compared using a general linear model considering as factors the crank system and workload with post hoc analysis at α=0.05. RMS presented effect of workload, but no effect of crank system was found for the muscles analyzed. The present results do not support effects of the noncircular crank system on variables of performance and muscle activation during incremental cycling in trained mountain bike cyclists.

Influence of leg preference on bilateral muscle activation during cycling.

The purpose of this study was to investigate asymmetry of muscle activation in participants with different levels of experience and performance with cycling. Two separate experiments were conducted, one with nine cyclists and one with nine non-cyclists. The experiments involved incremental maximal and sub-maximal constant load cycling tests. Bilateral surface electromyography (EMG) and gross and net muscle efficiency were assessed. Analyses of variance in mixed linear models and t-tests were conducted. The cyclists in Experiment 1 presented higher gross efficiency (P < 0.05), whereas net efficiency did not differ between the two experiments (21.3 ± 1.4% and 19.8 ± 1.0% for cyclists and non-cyclists, respectively). The electrical muscle activity increased significantly with exercise intensity regardless of leg preference in both experiments. The coefficient of variation of EMG indicated main effects of leg in both experiments. The non-preferred leg of non-cyclists (Experiment 2) presented statistically higher variability of muscle activity in the gastrocnemius medialis and vastus lateralis. Our findings suggest similar electrical muscle activity between legs in both cyclists and non-cyclists regardless of exercise intensity. However, EMG variability was asymmetric and appears to be strongly influenced by exercise intensity for cyclists and non-cyclists, especially during sub-maximal intensity. Neural factors per se do not seem to fully explain previous reports of pedalling asymmetries.

Does leg preference affect muscle activation and efficiency?

The aim of this study was to investigate the effect of leg preference and cycling experience on unilateral muscle efficiency and muscle activation. To achieve this purpose, two experiments were performed. Experiment 1 involved eight cyclists and experiment 2 included eight non-cyclists. Subjects underwent an incremental maximal test and submaximal trials of one-legged cycling for preferred and non-preferred leg. Oxygen uptake and muscle efficiency were compared between legs. The magnitude of muscle activation (RMS) and the inter-limb excitation were monitored for the vastus lateralis, biceps femoris and gastrocnemius (medial head) muscles during one-legged cycling with preferred and non-preferred leg. Variables of muscle activation, oxygen uptake and muscle efficiency (gross and net) did not differ between legs (P>0.05). The magnitude of muscle activation and its variability were similar between legs while performing the unilateral pedaling. Inter-limb communication did not differ between experiments (P>0.05). Similar activation between legs was consistent with the influence of bilateral practice for attaining similar performance between sides. These results do not support asymmetry in magnitude of muscle activation during pedaling.

Cycling with noncircular chainring system changes the three-dimensional kinematics of the lower limbs.

This study investigated the three-dimensional (3-D) pedaling kinematics using a noncircular chainring system and a conventional system. Five cyclists pedaled at their preferred cadence at a workload of 300 W using two crank systems. Flexion/extension of the hip, knee and ankle as well as shank rotation, foot adduction/abduction, and pedal angle were measured. Joint range of motion (ROM) and angular displacements were compared between the systems. Sagittal plane ROM was significantly greater (P < 0.05) at the hip (noncircular system = 39 +/- 3 degrees; conventional system = 34 +/- 4 degrees) the knee (noncircular system = 69 +/- 4 degrees; conventional system = 57 +/- 10 degrees), and ankle (noncircular system = 21 +/- 2 degrees; conventional system = 19 +/- 4 degrees) resulting in greater pedal ROM (noncircular system = 43 +/- 3 degrees; conventional system = 37 +/- 5 degrees) while using the noncircular system. Shank rotation ROM was significantly lower (P < 0.05) while using the noncircular chainring (noncircular system = 10 +/- 1 degree; conventional system = 14 +/- 1 degree). These results support a significant effect of the noncircular chainring system on pedaling kinematics during submaximal exercise.