Sara Horne

EFFECT OF CONTRACTION MODE OF SLOW-SPEED RESISTANCE TRAINING ON THE MAXIMUM RATE OF FORCE DEVELOPMENT IN THE HUMAN QUADRICEPS

This study examined the effects of slow‐speed resistance training involving concentric (CON, n = 10) versus eccentric (ECC, n = 11) single‐joint muscle contractions on contractile rate of force development (RFD) and neuromuscular activity (EMG), and its maintenance through detraining. Isokinetic knee extension training was performed 3 · week−1 for 10 weeks. Maximal isometric strength (+11.2%) and RFD (measured from 0–30/50/100/200 ms, respectively; +10.5%–20.5%) increased after 10 weeks (P < 0.01–0.05); however, there was no effect of training mode. Peak EMG amplitude and rate of EMG rise were not significantly altered with training or detraining. Subjects with below‐median normalized RFD (RFD/MVC) at 0 weeks significantly increased RFD after 5‐ and 10‐weeks training, which was associated with increased neuromuscular activity. Subjects who maintained their higher RFD after detraining also exhibited higher activity at detraining. Thus, only subjects with a lesser ability to rapidly attain their maximum force before training improved RFD with slow‐speed resistance exercise. Muscle Nerve, 2008

Changes in muscle force-length properties affect the early rise of force in vivo.

Changes in contractile rate of force development (RFD), measured within a short time interval from contraction initiation, were measured after a period of strength training that led to increases in muscle fascicle length but no measurable change in neuromuscular activity. The relationship between training‐induced shifts in the moment–angle relation and changes in RFD measured to 30 ms (i.e., early) and 200 ms (i.e., late) from the onset of isometric knee extension force were examined; shifts in the moment–angle relation were used as an overall measure of changes in quadriceps muscle fascicle length. A significant proportion of the variance in RFD measured only in the initial contraction phase (0–30 ms) could be explained by shifts in the moment–angle relation (r = −0.66–0.71; R2 = 0.44–0.50). Training‐induced increases in muscle fascicle length may lead to a reduced or complete lack of adaptive gains in contractile RFD, especially in the early contraction phase. Muscle Nerve 39: 512–520, 2009

Leg stiffness in human running: Comparison of estimates derived from previously published models to direct kinematic-kinetic measures.

It is not presently clear whether mathematical models used to estimate leg stiffness during human running are valid. Therefore, leg stiffness during the braking phase of ground contact of running was calculated directly using synchronous kinematic (high-speed motion analysis) and kinetic (force platform) analysis, and compared to stiffness calculated using four previously published kinetic models. Nineteen well-trained male middle distance runners (age=21.1±4.1yr; VO(2max)=69.5±7.5mlO(2)kg(-1)min(-1)) completed a series of runs of increasing speed from 2.5 to 6.5ms(-1). Leg stiffness was calculated directly from kinetic-kinematic analysis using both vertical and horizontal forces to obtain the resultant force in the line of leg compression (Model 1). Values were also estimated using four previously published mathematical models where only force platform derived and anthropometric measures were required (Models 2-5; Morin et al., 2005, Morin et al., 2011, Blum et al., 2009, Farley et al., 1993, respectively). The greatest statistical similarity between leg stiffness values occurred with Models 1 and 2. The poorest similarity occurred when values from Model 4 were compared with Model 1. Analyses suggest that the poor correlation between Model 1 other models may have resulted from errors in the estimation in change in leg length during the braking phase. Previously published mathematical models did not provide accurate leg stiffness estimates, although Model 2, used by Morin et al. (2005), provided reasonable estimates that could be further improved by the removal of systematic error using a correction factor (K=1.0496K(Model2)).

Development of lower limb stiffness and its contribution to maximum vertical jumping power during adolescence

SUMMARY Maximum power production during multi-joint tasks increases as children grow older. Previous research suggests that in adults, maximum power production in jumping is related to lower limb stiffness. In a developmental context, the question arises as to whether the relationship between maximum power production and lower limb stiffness is age-dependent. The purpose of this study was to investigate the relationship between lower limb stiffness and peak power production in adolescents (AD) and pre-adolescents (PA). With institutional approval, two groups of pre-adults (pre-adolescents: 11–13 years of age, N=43; adolescents: 16–18 years of age, N=30) performed 30 two-legged hops at their preferred frequency and three maximum counter-movement jumps. AD produced significantly greater peak power during the counter-movement jump than PA (t71=–5.28, P<0.001) even when body mass was accounted for. Lower limb stiffness was significantly correlated with peak power production during the counter-movement jump in AD (R=0.62, P<0.001) but not in PA (R=0.26, P=0.10). When normalised to body mass, the relationship between lower limb stiffness and peak power also differed between the two age groups (R=0.30, P=0.11 for AD and R=0.02, P=0.88 for PA). In addition, we found that during hopping, both PA and AD behaved like a simple spring-mass system. Our findings highlight the importance of lower limb stiffness in the context of muscular power production during multi-joint tasks. They let us speculate that during adolescence, children acquire the ability to take greater advantage of elastic energy storage in the musculotendinous system when performing maximum counter-movement jumps.

Attentional capture by spoken language: effects on netballers’ visual task performance

Abstract In two experiments, participants performed visual detection, visual discrimination and decision-making tasks, in which a binary (left/right) response was required. In all experimental conditions, a spoken word (“left”/“right”) was presented monaurally (left or right ear) at the onset of the visual stimulus. In Experiment 1, 26 non-athletes located a target amongst an array of distractors as quickly as possible, in both the presence and absence of spoken cues. Participants performed superiorly in the presence of valid cues, relative to invalid-cue and control conditions. In Experiment 2, 42 skilled netballers completed three tasks, in randomised order: a visual detection task, a visual discrimination task and a netball decision-making task – all in the presence of spoken cues. Our data showed that spoken auditory cues affected not only target detection, but also performance on more complex decision-making tasks: cues that were either spatially or semantically invalid slowed target detection time; spatially invalid cues impaired discrimination task accuracy; and cues that were either spatially or semantically valid improved accuracy and speeded decision-making time in the netball task. When studying visual perception and attention in sport, the impact of concomitant auditory information should be taken into account in order to achieve a more representative task design.

Study on Relationship between Foot Pressure Pattern and Hallux Valgus (HV) Progression

Hallux valgus is one of the most common foot deformities. Plantar pressure technologies are used widely for determination of biomechanical changes in foot during walking. There are already published claims relating to the pressure distribution of HV condition. However some of these claims are disputed and challenged. Although, disputed or otherwise, association of HV to sole pressure widely presented as a means of identifying such condition. Or knowing that HV exist, establishing what kind of pressure variation is expected may lead to better foot wear design for HV patients. Despite of extensive work on sole pressure patterns of patients, there has been no reported work found on conditions which leads to HV. Considering the fact that 23% of adults develop such condition during their life time, understanding HV is badly needed.