This thesis investigated a range of interdependent themes. There were two central questions. The first addressed whether visual information for the control of skilled actions is transformed and represented in a similar fashion as that used to represent the world for perception. The second addressed the nature of the visual information used in the control of reaching and grasping movements. A MacReflex (Qualisys AB) motion analysis system was used to measure kinematic parameters of reaches to real-world objects in a variety of situations. The results of the first empirical chapter, which explored the effects of pre-response delay on performance on various perception- and action-based tasks, supported Milner and Goodale's (1995) contention that visual processing for perception and for the control of action are segregated in two quasi-independent processing streams. Three further empirical chapters investigated the importance of binocular cues relative to monocular pictorial cues in the control of prehensile movements. Binocular cues were found to be sufficient but not necessary for the control of reliable reaches, both when reaching to single objects in isolation and when reaching into multiple-object scenes. This finding questions the current view that they play a primary role in the control of reliable reaches. Height in the visual field, which can, in principle, specify metric properties of the scene, was also found to be sufficient to support reliable reaching. The final empirical chapter addressed the implications of restricting peripheral information for estimates of distance and size used in the control of reaches. It was found that restricting the field of view resulted in underestimates of object distance although estimates of size were unchanged. In summary, the findings reported in this thesis support the dissociation between visual processing for perception and action, as proposed by Milner and Goodale (1995) and suggest that a variety of binocular and monocular sources of information are used in the control of natural reaching and grasping movements.

No description available.

Grasping and functionally interacting with a relatively large or awkwardly shaped object requires the independent and cooperative coordination of both limbs. Acknowledging the vital role of visual information in successfully executing any prehensile movements, the present study aimed to clarify how well existing bimanual coordination models (Kelso et al, 1979; Marteniuk & Mackenzie, 1980) can account for bimanual prehension movements targeting a single end-point under varying visual conditions. We therefore, employed two experiments in which vision of the target object and limbs was available or unavailable during a bimanual movement in order to determine the affects of visual or memory-guided control (e.g. feedback vs. feed forward) on limb coordination.<p>Ten right-handed participants (mean age = 24.5) performed a specific bimanual prehension movement targeting a solitary, static object under both visual closed loop (CL) and open loop 2s delay (OL2) conditions. Target location was varied while target amplitude remained constant. Kinematic data (bimanual coupling variables) indicated that regardless of target location, participants employed one of two highly successful movement execution strategies depending on visual feedback availability. During visual (CL) conditions participants employed a dominant-hand initiation strategy characterized by a significantly faster right-hand (RH) reaction time and simultaneous hand contact with the target. In contrast, when no visual feedback was available (OL2), participants utilized a search and follow strategy characterized by limb coupling at movement onset and a reliance on the dominant RH to contact the target ~62 ms before the left.<p>In conclusion, the common goal parameters of targeting a single object with both hands are maintained and successfully achieved regardless of visual condition. Furthermore, independent programming of each limb is undeniably evident within the behaviours observed providing support for the neural cross-talk theory of bimanual coordination (Marteniuk & Mackenzie, 1980). Whether movement execution is visually (CL) or memory-guided (OL2) there is a clear preference of RH utilization possibly due to its dynamic and/or hemispheric advantages in controlling complex motor behaviours (Gonzalez et al., 2006). Therefore, we propose that bimanual grasping to a solitary target is possibly governed globally by a higher-level structure and successful execution is achieved via independent spinal pathway modulation of limbs.

Grasping and functionally interacting with a relatively large or awkwardly shaped object requires the independent and cooperative coordination of both limbs. Acknowledging the vital role of visual information in successfully executing any prehensile movements, the present study aimed to clarify how well existing bimanual coordination models (Kelso et al, 1979; Marteniuk & Mackenzie, 1980) can account for bimanual prehension movements targeting a single end-point under varying visual conditions. We therefore, employed two experiments in which vision of the target object and limbs was available or unavailable during a bimanual movement in order to determine the affects of visual or memory-guided control (e.g. feedback vs. feed forward) on limb coordination.<p>Ten right-handed participants (mean age = 24.5) performed a specific bimanual prehension movement targeting a solitary, static object under both visual closed loop (CL) and open loop 2s delay (OL2) conditions. Target location was varied while target amplitude remained constant. Kinematic data (bimanual coupling variables) indicated that regardless of target location, participants employed one of two highly successful movement execution strategies depending on visual feedback availability. During visual (CL) conditions participants employed a dominant-hand initiation strategy characterized by a significantly faster right-hand (RH) reaction time and simultaneous hand contact with the target. In contrast, when no visual feedback was available (OL2), participants utilized a search and follow strategy characterized by limb coupling at movement onset and a reliance on the dominant RH to contact the target ~62 ms before the left.<p>In conclusion, the common goal parameters of targeting a single object with both hands are maintained and successfully achieved regardless of visual condition. Furthermore, independent programming of each limb is undeniably evident within the behaviours observed providing support for the neural cross-talk theory of bimanual coordination (Marteniuk & Mackenzie, 1980). Whether movement execution is visually (CL) or memory-guided (OL2) there is a clear preference of RH utilization possibly due to its dynamic and/or hemispheric advantages in controlling complex motor behaviours (Gonzalez et al., 2006). Therefore, we propose that bimanual grasping to a solitary target is possibly governed globally by a higher-level structure and successful execution is achieved via independent spinal pathway modulation of limbs.

La préhension manuelle, impliquée dans l’acquisition de nourriture et la locomotion, est commune à tous les primates. Toutefois, les mécanismes de son émergence et de son évolution restent encore à élucider. Quels sont les facteurs 1) écologiques (propriétés de la nourriture et du substrat) conduisant à une plus grande utilisation de la main chez les premiers primates et 2) fonctionnels (posture corporelle, cinématique du membre supérieur) impliqués dans l’évolution de la préhension des primates?Afin d’apporter des éléments de réponse, cette thèse a pour objectif de déterminer les stratégies comportementales et cinématiques de la préhension non contrainte d’espèces représentatives des grands groupes phylogénétiques primates (microcèbe, lémur catta, capucin, gorille, chimpanzé, humain).Tout d’abord, les stratégies comportementales du microcèbe, présentant des convergences avec les premiers primates, suggèrent que l’arboricolie et l’omnivorie ont joué un rôle important dans l’émergence des capacités de préhension des primates. Ensuite, l’analyse de la préhension du gorille et de l’humain montre une influence limitée des postures corporelles sur les stratégies articulaires du membre supérieur. Enfin, la comparaison de toutes les espèces montre que certains invariants cinématiques de la préhension liés à la vitesse du poignet existent indépendamment des espèces et que d’autres semblent être lié au comportement des espèces. En outre, deux stratégies articulaires divisent les espèces favorisant les rotations (gorille et chimpanzé) de celles privilégiant les flexions-extensions (lémur, capucin, humain). Ces stratégies articulaires semblent avoir évolué indépendamment de leurs capacités préhensiles.L’ensemble de ces résultats est discuté au regard des données comportementales et fonctionnelles connues et confronté aux théories actuelles sur l’origine et l’évolution de la préhension. / Manual prehension, involved in food acquisition and locomotion, is common to all primates. However, the mechanisms of its emergence and evolution still remain to be elucidated. This prompts questions such as 1) what are the ecological factors (food and substrate properties) leading to an increase of the use of the hand in early primates, and 2) what functional factors (body posture, kinematics of the forelimb) are involved in the evolution of prehension in primates?The thesis project aims to determine the behavioural and kinematic strategies of unconstrained prehension in representative species of the major lineages of primates (the mouse lemur, lemur catta, capuchin, gorilla, chimpanzee, human).The behavioural strategies of the mouse lemur, convergent on early primates, suggest that arboreality and omnivory have played an important role in the origin of prehensile abilities in primates. The analysis of prehension in gorillas and humans shows a limited influence of body posture on the angular joint excursions and kinematic strategies. A comparison of all the species reveals that some kinematic invariants in the wrist velocity profile exist, independent of the species. Yet others appear to be related to the specific behaviour of the species. Moreover, two joint motion strategies divide the species, one favoring the rotations (gorillas and chimpanzees) and one involving more flexion-extension movements (lemurs, capuchins, humans). These joint motion strategies seem to have evolved independently of grasping ability.The results are discussed in the context of current work and theories on the origin and the evolution of prehension in primates.

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

The dexterity of the human hand depends largely on the ability to move the fingers independently, the execution of which requires the coordination of multiple muscles. How these muscle ensembles are recruited by the central nervous system is not clear. Therefore, the objective of this dissertation was to identify some of the neural mechanisms whereby certain hand muscles are recruited into functional groups, or muscle synergies, needed for the generation of specific hand and finger movements.We characterized the organization of synaptic inputs onto the motor neurons supplying different compartments of a multi-tendoned finger flexor, the flexor digitorum superficialis (FDS). We found that the motor neurons controlling different finger compartments of the FDS do not receive entirely segregated inputs, and that the motor neurons supplying adjacent compartments receive substantially more common synaptic input than motor neurons supplying compartments further apart. The FDS and another multi-tendoned finger flexor, the flexor digitorum profundus (FDP), both insert onto each finger and function together to flex the fingers. Surprisingly, we found that the motor neurons controlling the compartments of FDS and FDP to the same finger receive completely independent inputs, despite similar mechanical functions of the two muscles. Thus, there is more neural coupling between motor neurons supplying compartments of the same muscle that move different fingers than there is between motor neurons supplying the compartments of two different muscles that move the same finger.Although the motor neurons supplying the flexors of the tips of the thumb [flexor pollicis longus (FPL)] and index finger [index compartment of the flexor digitorum profundus (FDP2)] receive substantial shared synaptic input during a precision grip task, the removal of the normal tactile feedback from the digit pads did not change the amount of common input to the two motor neuron pools, indicating these last-order divergent neurons do not require tactile afferent inputs for activation. Finally, in contrast to the substantial shared input to motor neurons supplying these two extrinsic muscles (FPL and FDP2), the motor neurons supplying two intrinsic muscles of the thumb [adductor pollicis (AdP)] and index finger [first dorsal interosseous (FDI)] were shown to receive few shared inputs during precision grip.

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

Les travaux portant sur l’imagerie motrice (IM) ont montré l’identité des processus de production réelle et de représentation mentale du mouvement. Diverses voies expérimentales incluant la chronométrie mentale, les indices physiologiques (dont ceux issus de la neuroimagerie) ont été utilisées pour montrer que la représentation mentale de l’action repose sur les mêmes mécanismes que la préparation motrice et agirait sur la plasticité cérébrale. Le rôle de l’IM dans l’amélioration et l’apprentissage du mouvement, la récupération motrice après une lésion des effecteurs musculo-articulaires a été démontré chez le sujet sain. L’entraînement mental pourrait donc être intégré dans les protocoles thérapeutiques suite à une lésion centrale ou périphérique. Si plusieurs expériences ont montré son efficacité lorsqu’il est pratiqué après un accident vasculaire cérébral, aucune étude n’a porté sur son rôle dans la réadaptation fonctionnelle du patient médullo-lésé. L’hypothèse est que l’entraînement par IM associé à la rééducation classique peut facilement être intégrer dans les protocoles de réadaptation de ces patients et favoriserait la récupération et l’amélioration de la préhension chez les patients tétraplégiques / The mental representation of movement may help motor functions recovery after central or peripheral stroke. There is now ample evidence that motor performance and learning ma benefit from mental rehearsal in healthy subjects. However, whether the ability to perform motor imagery is preserved after spinal cord injury, the effectiveness of mental rehearsal on prehension rehabilitation has to be questioned. The review of relevant literature about motor imagery and rehabilitation show that integrating mental practice into the rehabilitation process may be a reliable tool. Traditional stroke rehabilitation therapies are usually based upon actual movement aimed at improving motor functions. However, this may be limited by muscle spasticity, muscle weakness, or persistent deficit in movement coordination. As motor imagery and actual movement share the same neural substrate, mental rehearsal may serve motor rehabilitation by involving cerebral plasticity and thus facilitating recovery. More specifically, it will be useful to elaborate guideline of mental practice in rehabilitation. Additional clinical issues, including brain mapping studies, need to be performed

O movimento de alcançar e de pegar objetos é amplamente utilizado nas atividades diárias. Desta forma, diversos estudos têm analisado e descrito este padrão de movimento em função de diferentes aspectos que influenciam seu controle. Da mesma forma, o movimento de andar é uma habilidade fundamental nas atividades diárias e tem sido estudado e descrito amplamente na literatura. Entretanto, pouco se sabe sobre quais são as alterações que ocorrem nessas habilidades motoras quando elas são combinadas. A realização combinada de habilidades motoras (ex., andar e pegar um objeto) está muito presente no dia a dia das pessoas, mas o entendimento do controle desse tipo de tarefa combinada ainda não foi elucidado. Adicionalmente, ainda não está claro quais são as modificações que ocorrem nestes movimentos em função do processo de envelhecimento e do histórico de quedas recentes em idosos. Desta forma, três estudos foram conduzidos para investigar o desempenho motor de adultos jovens e idosos com e sem histórico de quedas na marcha combinada com o movimento de preensão em função do nível de dificuldade da tarefa manual. O primeiro estudo investigou o desempenho motor dos adultos jovens na marcha combinada com o movimento de preensão. O segundo estudo comparou o desempenho motor entre idosos com e sem histórico de quedas na marcha combinada com o movimento de preensão. Ainda, o terceiro estudo comparou o padrão de coordenação entre idosos (com e sem histórico de quedas) e adultos jovens na marcha combinada com o movimento de preensão. Participaram desta tese, 45 indivíduos distribuídos em três grupos (n=15): adultos jovens, idosos sem histórico de quedas e idosos com histórico de quedas. Os indivíduos foram convidados a alcançar e pegar um objeto em duas tarefas (manutenção da postura ereta e marcha) e para cada uma, seis condições experimentais foram realizadas com diferentes níveis de dificuldade. Para analisar o movimento de preensão, movimentos do corpo todo e os parâmetros espaço-temporais da marcha, um sistema tridimensional de análise de movimento foi utilizado. Modificações na marcha e no movimento de preensão foram identificados quando combinados, especialmente para as condições mais desafiadoras da tarefa manual. A adição da tarefa de pegar o objeto provocou uma adaptação na marcha, pois os participantes adotaram uma estratégia mais conservadora para aumentar a estabilidade dinâmica durante a fase de aproximação. Assim é possível sugerir que o movimento de preensão foi sobreposto ao da marcha, embora as adaptações no comportamento motor sejam globais, pois ambos os padrões motores (marcha e preensão) foram modificados para realizar com sucesso a tarefa em função dos diferentes níveis de dificuldade da tarefa manual. Os idosos com histórico de quedas apresentaram um desempenho motor inferior aos idosos sem histórico de quedas na marcha combinada com o movimento de preensão, como por exemplo, redução na velocidade do passo, aumento na duração do passo, redução na velocidade do punho e na abertura entre os dedos. Além disso, os idosos com histórico de quedas apresentaram maior redução na velocidade do COM AP em comparação com os idosos sem histórico de quedas. Assim, o paradigma de tarefas combinadas desenvolvido no presente estudo identificou mudanças nas estratégias de controle motor em idosos caidores, sendo que estas alterações foram ainda mais evidenciadas nas condições manuais mais difíceis. Ainda, a adição da tarefa de pegar o objeto na marcha modificou o padrão de coordenação entre membros superiores e inferiores para os movimentos de flexão/extensão e abdução/adução. Assim, para os movimentos de flexão e extensão, um padrão mais em fase e menos fora de fase foi identificado na condição de preensão comparado com a marcha livre quando o ombro direito foi analisado em relação ao ombro esquerdo e quadril direito. Para os movimentos de abdução e adução, quando o movimento de ombro direito foi analisado em relação ao ombro esquerdo e quadril direito, foi observado um padrão menos em fase. Além disso, um padrão menos fora de fase foi observado para os acoplamentos entre ombro direito-ombro esquerdo e ombro direito-quadril esquerdo. Entretanto, estas mudanças no padrão de coordenação não foram afetadas pelo nível de dificuldade manual. Este resultado sugere que as mudanças no padrão de coordenação são mais globais, enquanto mudanças específicas no movimento de membro superior são necessárias para acomodar as diferentes demandas da tarefa manual. Finalmente, idosos com histórico de quedas apresentaram um padrão diferente de coordenação quando comparados com os adultos jovens, como por exemplo, um padrão mais fora de fase para o acoplamento entre ombro direito e quadril direito e um padrão menos fora de fase para o acoplamento entre ombro direito e quadril esquerdo na marcha combinada com o movimento de preensão. Desta forma, parece que os idosos com histórico de quedas desacoplam a tarefa da marcha combinada com o movimento de preensão, diferentes dos adultos jovens e idosos sem histórico de quedas. / Reaching-to-grasping an object is widely used in daily activities. Many studies have analyzed and described this movement pattern considering different aspects that influence how it is controlled. Likewise, walking is a fundamental skill in daily activities and has been studied and described widely in the literature. However, little is known about what are the changes that occur in these motor skills when they are combined. The combined performance of motor skills (e.g. walk and grasp an object) is very common in daily life activities, but the understanding of the control mechanisms of this type of task is lacking. In addition, it is not clear what are the changes that occur in these movements due to aging and changes in balance control as observed in older adults with history of falls. Thus, three studies were designed to investigate the motor performance of young adults and older adults with and without history of falls during walking combined with prehension. The first study investigated motor performance of young adults while performing the combined task of walk and prehension at different levels of difficulty of the manual task. The second study investigated the same combined task with different levels of manual task difficulty in older adults with and without history of falls. Yet, the third study investigated the interlimb coordination pattern in young and older adults with and without history of falls during the combined task of walking and prehension with different levels of manual task difficulty. Forty-five individuals, distributed in three groups (young adults; older adults without history of falls; older adults with history of falls), participated in this study. They performed the reach-to-grasp movement in two tasks (upright stance and gait) involving six experimental condition with different levels of manual difficulty. To analyze prehension, body movements and spatio-temporal gait parameters, a tridimensional movement analysis system was used. Modifications in gait and prehension were identified when they were combined, especially for the most difficult prehension conditions. The grasping task caused an adaptation in gait since participants preferred to adopt a more conservative strategy, increasing their dynamic stability during the approach phase and when grasping the dowel. Based on these results, it is possible to suggest that prehension was superimposed on gait, although the adaptations in motor behavior were global, since both motor patterns (i.e., walking and prehension) were changed to perform the task successfully with different levels of difficulty. It is possible to suggest that motor performance of fallers in the combined task of walking and grasping is more impaired than in no-fallers (for instance, decreased step velocity, increased step duration, decreased wrist velocity and peak grip aperture velocity). Moreover, older adults with history of falls presented a greater reduction in COM AP velocity when compared to older adults without history of falls. The combined task paradigm used in the present study showed some changes in motor control strategy of fallers older adults when performing walking and prehension combined. In addition, motor patterns (walking and grasping) of older adults (fallers and no-fallers) were modified in function of the level of manual task difficulty. The analysis of the relative motion allowed the quantification of the changes in the coordination pattern of the combined task involving walking and prehension for flexion/extension and abduction/adduction movements. For flexion/extension movements, a more in-phase and a less anti-phase pattern was identified in the grasping condition compared to walking through when right shoulder was analyzed relative to left shoulder and right hip. For adduction/abduction movements, when right shoulder was analyzed relative to left shoulder and right hip, it was observed less in phase pattern. In addition, we found a less anti-phase pattern for right shoulder-left shoulder and right shoulder-left hip couplings. However, the changes in motor coordination were not affected by the manual task difficulty for young adults and older adults with and without history of falls. This result suggests that changes in coordination are more general while specific changes in upper limb movement are necessary to deal with different task demands. Finally, older adults with history of falls presented a different pattern of coordination than young adults, such as, a more anti-phase pattern for right shoulder-right hip coupling and a less anti-phase pattern for right shoulder-left hip coupling during the combined task. Thus, it seems that older adults with history of falls decouple the walking and prehension tasks, differently of young adults and older adults without history of falls.