Purpose: Monitor changes in force production, running economy (RE), and running kinematics (RK) in a highly trained marathon runner after beginning a strength training (ST) program. Methods: One marathon runner (M, 27 y, 165 cm, 53.3 kg, VO2pesk 67.43 ml/kg/min, PR 2:33:13) with no history of ST completed a 12-week block periodized ST program. Baseline and reliability testing was conducted over a two-month period prior to ST. The completed ST RPE and work (volume load*displacement) and running volume (km/wk) were monitored over the 12 weeks. The athlete performed an isometric mid-thigh pull to assess peak force (PF, N), rate of force development at 250 ms (RFD250), and net impulse at 250 ms (NI250) during baseline and throughout ST. The athlete performed a steady state test on a treadmill instrumented with the OptojumpTM optic sensor system to assess RE (ml/kg/km) and RK during baseline and throughout ST. Impact of the ST program was assessed by percent change of the variables during the taper from the baseline average and by the odds of a true change using the typical error and smallest worthwhile change. Results: PF improved (120:1 odds) by 17.11%, RFD250 improved (22:1 odds) by 24.73%, and NI250 improved (10:1 odds) by 16.70% before competition. Ground contact time decreased (7:1 odds) by 2.57%, flight time decreased (1:1 odds) by 1.49%, step rate increased (2:1 odds) by 2.28%, and step length decreased (57:1: odds) by 2.21%. RE improved (3:1 odds) by 2.09%. Conclusion: Improving a runner’s maximal strength and rate of force development may positively influence RK and RE.

The purpose of this study was to evaluate the relationship between force production asymmetry and performance of athletes with differing strength levels in males and females. Collegiate athletes (n=129) from various sports were ranked according to isometric mid-thigh pull peak force and the top (‘strong’) and bottom (‘weak’) 25% were used for analysis. Symmetry index (SI) scores were calculated and correlated with their respective force-time characteristics using bivariate correlations. For the weaker males, several negative moderate correlations were observed; however, no statistically significant correlations were observed for the females in either group. These findings indicate that force production asymmetry is inversely related to performance in weaker male athletes during isometric strength testing; however, similar to previous findings, this relationship is not apparent in stronger males.

Caffeine is often used in a variety of forms to enhance athletic performance; however, research regarding caffeine’s effects on strength and power in female athletes is lacking. Therefore, the purpose of this study was to analyze the acute effects of caffeine anhydrous (6 mg/kg of body mass) on jumping performance and maximal strength in female collegiate athletes. Eleven athletes (19.7 ± 0.9 yrs; 166.4 ± 10.2 cm, 67.7 ± 9.4 kg) performed two testing sessions separated by one week, and randomly received caffeine or placebo using a double-blind approach. Heart rate, blood pressure, and tympanic temperature were recorded before athletes received each condition, following 60 min of quiet sitting, and directly after performance testing. Athletes were assessed on unweighted and weighted squat jump height (SJH0, SJH20) and countermovement jump height (CMJH0, CMJH20), isometric mid-thigh pull peak force (IPF), and rate of force development from 0–200 ms (RFD200). Resting systolic blood pressure was significantly greater following caffeine administration compared to a placebo (p = 0.017). There were small, significant differences in SJH0 (p = 0.035, g = 0.35), SJH20 (p = 0.002, g = 0.49), CMJH0 (p = 0.015, g = 0.19), and CMJH20 (p < 0.001, g = 0.37) in favor of caffeine over placebo. However, there was no significant difference in IPF (p = 0.369, g = 0.12) and RFD200 (p = 0.235, g = 0.32) between conditions. Therefore, caffeine appears to enhance jumping performance, but not maximal strength in female collegiate athletes.

<p>Many daily motor tasks involve the precise control of both force level and motor timing. The neural mechanisms concurrently managing these movement parameters remain unclear, as the dominant focus of previous literature has been to examine each in isolation. As a result, little is understood regarding the contribution of various sensory modalities to force output and interval production in sequential motor tasks. This thesis uses a sequential force production task to investigate the roles of visual and somatosensory feedback in the timed control of force. In Chapter 2 we find that removal of visual force feedback resulted in specific force output errors, but leaves motor timing behavior relatively unaffected according to predictions of the two-level timing model by Wing and Kristofferson (1973). In Chapter 3, we show that force output errors exhibited in the absence of a visual reference may be related to the processing of reafferent somatosensation from self-generated force pulses. The results of Chapter 4 reveal evidence that force errors exhibited following visual feedback removal are consistent with a shift in the perceived magnitude of force output and that the direction of error may be determined by prior task constraints. In Chapter 5 we find evidence of effector-specificity in the processing of and compensation for reafferent somatosensation. Lastly, in Chapter 6 we find that the interplay between audition and somatosensation in the control of sound level by the vocal effectors resembles that which is observed between vision and somatosensation in the control of force by the distal effectors.</p> / Doctor of Philosophy (PhD)

Mon travail fut de développer différents projets en vue de mieux comprendre la dynamique et l'organisation des réseaux d'actine et les mécanismes moléculaires à l'origine de la production de force, cela en systèmes reconstitués bio-mimétiques. Dans un premier temps je me suis intéressée à l'étude de l'organisation spatio-temporelle des réseaux d'actine et de ses protéines associées durant la motilité de particules recouverte de promoteurs de nucléation (Achard et al, Current Biology, 2010 et Reymann et al, sous presse à MBOC). J'ai suivi en temps réel l'incorporation de deux régulateurs de l'actine (capping protein et ADF/cofiline) et montré que leur contrôle biochimique sur l'actine gouverne également ces propriétés mécaniques. Afin de mieux caractériser les propriétés mécaniques de ces réseaux d'actine en expension, j'ai ensuite développé un système biomimétique novateur utilisant un set-up de micro-patterning permettant un contrôle spatial reproductible des sites de nucléation d'actine. Cela m'a permis de montrer comment des barrières géométriques, semblables à celles trouvées dans les cellules, peuvent influencer la formation dynamique de réseaux organisés d'actine et ainsi contrôler la localisation de la production de forces. (Reymann et al, Nature Materials, 2010). De plus l'addition de moteurs moléculaires sur ce système versatile nous a permis d'étudier la contraction induite par des myosines. En particulier les myosines VI-HMM interagissent de manière sélective sur différentes architectures d'actine (organisation parallèle ou antiparallèle, réseau enchevêtré), aboutissant à un processus en trois phase : tension puis déformation des réseaux d'actine fortement couplé à un désassemblage massif des filaments. Ce phénomène est intimement dépendant de l'architecture du réseau d'actine et pourrait donc jouer un rôle essentiel dans la régulation spatiale des zones d'expansion et de contraction du cytosquelette in vivo. (Travail en cours d'écriture). / I have developed different projects in order to tackle the problem of actin network dynamics and organization as well as the molecular mechanism at the origin of force production in biomimetic reconstituted systems. My first interest concerned the spatiotemporal organization of actin networks and actin-binding proteins during actin based motility of nucleation promoting factor-coated particles (Achard et al, Current Biology, 2010 and Reymann et al, in press at MBOC). I tracked in real time the incorporation of two actin regulators and showed that their biochemical control of actin dynamics also governs its mechanical properties. To further characterize mechanical properties of expanding actin networks, I used an innovative micro-patterning set-up allowing a reproducible spatial control of actin nucleation sites. It allowed me to show that geometrical boundaries, such as those encountered in cells, affect the dynamic formation of highly ordered actin structures and hence control the location of force production (Reymann et al, Nature Materials, 2010). Finally the addition of molecular motors on this tunable system allowed me to study implications for myosin-induced contractility. In particular, HMM-MyosinVI selectively interact with the different actin network architectures (parallel, anti-parallel organization or entangled networks) and leads to a selective three-phase process of tension, deformation of actin networks tightly coupled to massive filament disassembly. This phenomenon being highly dependent on actin network architecture could therefore play an essential role in the spatial regulation of expanding and contracting regions of actin cytoskeleton in cells. (Work in writing process).

<div>Manual function is a key determinant of functional independence. It is well known that manual dexterity declines with aging and negatively impacts quality of life. Therefore, much work has focused on understanding the biomechanics and motor control of manual function in general, and the action of the fingers in particular. Previous research has revealed consistent patterns of interdependence in the action of the fingers that (1) alter with age, and (2) have consequences for manual control, and thereby manual function. Most of this previous work on finger behavior quantifies finger capacities and interactions in terms of maximal forces. However, activities of daily living likely require individuals to rapidly change forces more frequently than produce maximal forces. Therefore, the present work quantifies, for the first time, finger capacities and interactions during rapid increase and decrease in finger forces, and how these quantities change with age. </div><div><br></div><div>Young and older adults performed maximal force production tasks and also tasks that required them to rapidly increase or decrease finger forces from three initial force levels using multiple combinations of the fingers of their dominant hand. The maximal finger forces and force rates, and the interdependence of the fingers (enslaving, individuation, sharing, and deficit) during both behaviors are reported in detail. Overall, similarities in finger behavior patterns obtained from maximal force and maximal force rates were observed. However, some differences are also noted, and novel findings (especially, comparison between force increase and decrease) are reported. Finally, future work that may lead to clinical applications is discussed. </div>

Les moteurs moléculaires sont des protéines capables de produire une force : elles transforment l'énergie chimique de l'hydrolyse de l'ATP en énergie mécanique. Cette thèse se focalise sur l'étude d'une famille de moteurs moléculaires, les myosines, qui se déplacent le long des filaments d'actine et assurent d'importantes fonctions cellulaires.La myosine VI est une myosine très particulière car elle est la seule à se déplacer vers l'extrémité négative des filaments d'actine. Elle est produite dans la cellule sous forme auto-inhibée, inactive. Dans la cellule, son activité est également régulée par plusieurs protéines interagissant avec la queue C-terminale de la myosine VI. Ces protéines, présentes à des endroits précis de la cellule, recrutent la myosine VI et dictent l'action qu'elle doit effectuer. Des analyses de SAXS, de dispersion de la lumière, de microscopie, d'interaction et de mutagénèse ont permis de mieux comprendre le mécanisme régulant l'adoption de l'état auto-inhibé, ainsi que son activation par le calcium. L'interaction avec différents partenaires a été caractérisée. GIPC1, le partenaire le plus étudié, promeut de façon indirecte la dimérisation et l'activation de la myosine VI.Pendant ma thèse, j'ai également été impliqué dans deux autres projets qui s'inscrivent dans la logique du projet de thèse et qui ont mené à la publication de quatre articles. Deux chapitres, plus brefs, sont donc dédiés à ces projets. Le deuxième chapitre porte sur la régulation de l'activité de la myosine VII par ses partenaires cellulaires. Finalement, le troisième chapitre est dédié à l'étude de la modification allostérique de l'activité des myosines par des petites molécules. / Molecular motors are essential agents of force production in the cells: they convert the chemical energy released by the hydrolysis of ATP into mechanical work. This thesis focuses on myosins, a family of molecular motors responsible for actin-based motility. Myosin VI is unique among all of the myosin superfamily members in that it moves in the opposite direction of all other known myosins. Previous work revealed myosin VI tail ability to fold back, constituting a potential auto-inhibited state that prevents motor activity. Several myosin VI partners, binding to the C-terminal tail of the myosin, have been identified and shown to recruit the motor for different functions. In the first chapter of this thesis, the mechanism allowing the regulation of myosin VI activity has been studied using biochemical and biophysical analysis (SAXS, light scattering, microscopy, binding assays and mutagenesis). GIPC1, the most studied myosin VI partners, promotes myosin dimerization and activation. During my PhD, I have been also involved in two other projects, in line with my thesis project, that have led to the publication of four articles. Two shorter chapters are therefore devoted to these projects. The second chapter of my thesis explores myosin VII activity regulation by its cellular partners. Finally, the third chapter is devoted to the allosteric regulation of myosins activity by small molecules.

Chez les Vertébrés, le plan d’organisation du corps est mis en place lors de l’élongation de l’axe antéro-postérieur. L’importance du mésoderme pré-somitique (PSM) dans l’élongation a précédemment été démontrée chez l’embryon de poulet. Il a été proposé qu’un gradient de motilité cellulaire aléatoire, contrôlé par un gradient de morphogène, était nécessaire à l’élongation de l’axe. À ce jour, les interactions entre un profil de signalisation moléculaire bien connu et un mécanisme physique d’élongation restent à explorer. En particulier, plusieurs questions de mécanique doivent être étudiées. Tout d’abord, un gradient de motilité cellulaire peut-il provoquer l’extension du PSM ? Ensuite, la force générée par l’extension du PSM peut-elle être à l’origine de l’élongation de l’axe ? Enfin, comment l’extension du PSM est-elle couplée mécaniquement à l’élongation des autres tissus ? Pour répondre à ces questions, une meilleure description des propriétés mécaniques des tissus embryonnaires est nécessaire. De plus, afin d’estimer la contribution des différents tissus au processus d’élongation, une analyse quantitative de la production de force de ces tissus est essentielle. Dans cette thèse de doctorat, nous présentons le profil des propriétés visco-élastiques du PSM et du tube neural le long de l’axe. Nous démontrons également que des PSM isolés sont capables de s’allonger de manière autonome et nous mesurons leur contribution à la force totale d’élongation. / In vertebrates, the elongation of the anteroposterior axis is a crucial step during embryonic development as it results in the establishment of the basic body plan. A previous study highlighted the importance of the presomitic mesoderm (PSM) in elongation and showed that a gradient of random cell motility along the anteroposterior axis is necessary for proper elongation of the chicken embryo. It was proposed that a gradient of random cell motility, downstream of a morphogen gradient, drives axis extension. To date, the potential interaction between well-established molecular signaling and physical mechanisms involved in axis elongation remains largely unexplored. In particular, several mechanical questions need to be addressed. First, can the cell motility gradient lead to PSM extension? Second, is the force generated by PSM extension capable of promoting axis elongation? Third, how is PSM extension mechanically coupled with the elongation of all embryonic tissues? In order to tackle these questions, a better description of the mechanical properties of the embryonic tissues is required. Moreover, to assess specific tissues' contribution to elongation, a quantitative analysis of their force production is needed. In this Ph.D. thesis, we measure how the viscoelastic properties of both the PSM and the neural tube vary along the anteroposterior axis. We also demonstrate that isolated PSM explants are capable of autonomous elongation and we measure their contribution to the total force production in the embryo.

Abstract available in the Medicine and Science in Sports and Exercise.

Currently, multi-joint, position-specific isometric tests (MJIT) are commonly used as part of the monitoring of an athlete’s progress. Strong associations between isometric force-time curve parameters have been found. Perhaps the most commonly used test is the isometric mid-thigh pull (IMTP): the IMTP was created in the early 1990s and its use has grown considerably since that time. One sport in which it has been used extensively from the early 1990s to the present, particularly by the authors, is weightlifting. The relationships between weightlifting performance and IMTP force-time characteristics are quite strong, particularly for RFD. The IMTP is not only useful in assessing a weightlifter’s performance but can also be used for monitoring fatigue.