Asymmetric gait, or a difference in functioning between legs during human locomotion, is a health concern that can lead to secondary complications such as chronic musculoskeletal injury or a more sedentary lifestyle. Restoration of gait symmetry requires a gait adaptation, or a change in the way that an individual walks. Further knowledge of how to best promote a gait adaptation could lead to the creation of future rehabilitative protocols geared towards restoration of symmetric gait. To address this, a variable practice paradigm was implemented in able-bodied individuals walking asymmetrically on a split-belt treadmill. Individuals were assigned into one of three practice groups (from least variable to most: serial, random blocked, random) and walked on the treadmill for 720 strides of motor skill acquisition according to their given paradigm. They were asked to return 24 hours later and were given one of two tests for motor learning: retention or transfer. Three-dimensional kinematic and kinetic data were collected throughout the experimental protocol and used to analyze walking performance between the three practice groups. Results indicated that random blocked practice resulted in the best retention and transfer of mediolateral balance control variability, while serial practice had the highest variability on the transfer test. It was further demonstrated that this paradigm resulted in a unique mechanical strategy implemented by each practice group that further describes the role of variable practice in gait adaptation: random practice during acquisition, random blocked during retention, and serial during transfer. A principal component analysis showed that variable practice also results in the adoption of specific coordinative structuring of joint and segmental kinematics. These structures were mostly different across practice groups during the acquisition and retention phases. While it was generally hypothesized that random practice, which induces the highest amount of stepping errors during acquisition, would result in the best retention and transfer of the adapted gait pattern, this practice group did not perform as well as expected on the measured outcomes. Random blocked practice, on the other hand, may provide the optimal level of challenge and variability to best facilitate a gait adaptation. This dissertation includes previously published and unpublished co-authored material.

O objetivo desse estudo foi investigar os efeitos da liberdade na escolha das respostas, da variabilidade de resposta resultante dessa liberdade e da variabilidade externamente determinada no processo adaptativo em aprendizagem motora. Foram realizados oito experimentos, compostos por duas fases: estabilização, contendo 100 tentativas com conhecimento de resultados (CR), e adaptação, com 24 tentativas em uma mesma condição para todos os grupos, sem CR. Participaram do estudo 96 adultos de ambos os sexos, sem experiência prévia na tarefa utilizada. Como tarefa foi utilizada uma habilidade motora sequencial e de precisão temporal que consistiu em movimentar um cursor, usando o mouse, direcionando-o a seis alvos numa sequência, de forma que os \"toques\" nos alvos fossem realizados em coincidência com estímulos auditivos. A ordem dos toques na sequência foi livre nos grupos com liberdade na escolha das respostas e determinada nos grupos yokeds. Na fase de adaptação foi realizada uma modificação perceptivo-efetora na tarefa. O experimento 1 foi realizado para investigar o efeito da liberdade na escolha das respostas no processo adaptativo em aprendizagem motora. Os resultados evidenciaram que a liberdade na escolha da resposta, durante a fase de estabilização, beneficiou o processo adaptativo. O experimento 2 foi realizado para investigar o efeito da meta de aprendizagem nas escolhas dos aprendizes e no processo adaptativo em aprendizagem motora. Os resultados indicaram que a meta de aprendizagem teve efeito nas escolhas dos aprendizes, mas essas escolhas não ocasionaram superioridade nas medidas de desempenho na fase de adaptação. Houve menor tempo de planejamento da ação no primeiro bloco da fase de adaptação, indicando melhor preparação para uma nova situação nessa condição. Os experimentos 3 e 4 foram realizados para investigar o efeito da variabilidade de resposta resultante da condição de liberdade na escolha das respostas com meta de aprendizagem no processo adaptativo em aprendizagem motora. Os resultados desses dois experimentos apontaram que na presença da meta de aprendizagem, quando a liberdade na escolha das respostas é explorada ativa e efetivamente, o desempenho na fase de adaptação é favorecido, com indicativos de superioridade da condição com maior quantidade de variações na sequência quando comparada à condição com maior número de sequências utilizadas na fase de estabilização. Os experimentos 5 a 8 foram conduzidos para comparar o efeito da variabilidade resultante da liberdade na escolha das respostas com meta de aprendizagem com o da variabilidade externamente determinada no processo adaptativo em aprendizagem motora. Os resultados desses experimentos indicaram que a condição de liberdade na escolha das respostas com meta de aprendizagem não é suficiente para beneficiar o processo adaptativo. Quando a variabilidade de resposta resultante foi menor os benefícios da liberdade na escolha das respostas foram anulados, mas quando a variabilidade de resposta resultante foi maior os benefícios da liberdade na escolha das respostas foram igualados aos da variabilidade de resposta externamente determinada / The purpose of this study was to investigate the effects of freedom in response choice, variability resulting from this freedom, and externally determined variability on the adaptive process in motor learning. Eight experiments were carried out, each of them comprising two phases: stabilization, which consisted of 100 trials with knowledge of results (KR), and adaptation, with 24 trials in a same condition for all groups, without KR. Ninety-six adults of both sexes with no previous experience with the task took part in this study. The task consisted of a spatiotemporal sequential motor skill of moving a cursor, using the computer mouse, to six targets in sequence, so that the \"touches\" in the targets were performed in coincidence with auditory stimuli. The order of touches in the sequence was free for the groups with freedom in response choice and determined for the yoked groups. A perceptual-motor change in the task was introduced in the adaptation phase. The experiment 1 was conducted to investigate the effect of freedom in response choice on the adaptive process in motor learning. Results showed that freedom in response choice during the stabilization phase benefited adaptive process. The experiment 2 was conducted to investigate the effect of learning goal both on the learner\'s choice and on the adaptive process in motor learning. Results indicated that learning goal had an effect on learners\' choices, but these choices did not lead to superiority in performance measures during the adaptive phase. The results also showed less time for planning the action in the first block of adaptive phase, suggesting better preparation for a new situation in the learning goal condition. Experiments 3 and 4 were conduced to investigate the effect of response variability resulting from freedom in response choice with learning goal on the adaptive process in motor learning. Results of both experiments revealed that, with learning goal, when freedom in response choice is actively and effectively explored, performance in the adaptation phase is favored, with indicative of superiority of higher sequence variations condition over the higher number of sequences used condition in the stabilization phase. Experiments 5 to 8 were conduced to compare the effect of variability resulting from freedom in response choice, with learning goal, to the effect of externally determined variability on the adaptive process in motor learning. The results of these experiments indicated that freedom in response choice is not enough to benefit adaptive process. When response variability resulting from freedom was lower, the benefits were absent, but when it was higher, the benefits were matched to those of the externally determined response variability

O objetivo desse estudo foi investigar os efeitos da liberdade na escolha das respostas, da variabilidade de resposta resultante dessa liberdade e da variabilidade externamente determinada no processo adaptativo em aprendizagem motora. Foram realizados oito experimentos, compostos por duas fases: estabilização, contendo 100 tentativas com conhecimento de resultados (CR), e adaptação, com 24 tentativas em uma mesma condição para todos os grupos, sem CR. Participaram do estudo 96 adultos de ambos os sexos, sem experiência prévia na tarefa utilizada. Como tarefa foi utilizada uma habilidade motora sequencial e de precisão temporal que consistiu em movimentar um cursor, usando o mouse, direcionando-o a seis alvos numa sequência, de forma que os \"toques\" nos alvos fossem realizados em coincidência com estímulos auditivos. A ordem dos toques na sequência foi livre nos grupos com liberdade na escolha das respostas e determinada nos grupos yokeds. Na fase de adaptação foi realizada uma modificação perceptivo-efetora na tarefa. O experimento 1 foi realizado para investigar o efeito da liberdade na escolha das respostas no processo adaptativo em aprendizagem motora. Os resultados evidenciaram que a liberdade na escolha da resposta, durante a fase de estabilização, beneficiou o processo adaptativo. O experimento 2 foi realizado para investigar o efeito da meta de aprendizagem nas escolhas dos aprendizes e no processo adaptativo em aprendizagem motora. Os resultados indicaram que a meta de aprendizagem teve efeito nas escolhas dos aprendizes, mas essas escolhas não ocasionaram superioridade nas medidas de desempenho na fase de adaptação. Houve menor tempo de planejamento da ação no primeiro bloco da fase de adaptação, indicando melhor preparação para uma nova situação nessa condição. Os experimentos 3 e 4 foram realizados para investigar o efeito da variabilidade de resposta resultante da condição de liberdade na escolha das respostas com meta de aprendizagem no processo adaptativo em aprendizagem motora. Os resultados desses dois experimentos apontaram que na presença da meta de aprendizagem, quando a liberdade na escolha das respostas é explorada ativa e efetivamente, o desempenho na fase de adaptação é favorecido, com indicativos de superioridade da condição com maior quantidade de variações na sequência quando comparada à condição com maior número de sequências utilizadas na fase de estabilização. Os experimentos 5 a 8 foram conduzidos para comparar o efeito da variabilidade resultante da liberdade na escolha das respostas com meta de aprendizagem com o da variabilidade externamente determinada no processo adaptativo em aprendizagem motora. Os resultados desses experimentos indicaram que a condição de liberdade na escolha das respostas com meta de aprendizagem não é suficiente para beneficiar o processo adaptativo. Quando a variabilidade de resposta resultante foi menor os benefícios da liberdade na escolha das respostas foram anulados, mas quando a variabilidade de resposta resultante foi maior os benefícios da liberdade na escolha das respostas foram igualados aos da variabilidade de resposta externamente determinada / The purpose of this study was to investigate the effects of freedom in response choice, variability resulting from this freedom, and externally determined variability on the adaptive process in motor learning. Eight experiments were carried out, each of them comprising two phases: stabilization, which consisted of 100 trials with knowledge of results (KR), and adaptation, with 24 trials in a same condition for all groups, without KR. Ninety-six adults of both sexes with no previous experience with the task took part in this study. The task consisted of a spatiotemporal sequential motor skill of moving a cursor, using the computer mouse, to six targets in sequence, so that the \"touches\" in the targets were performed in coincidence with auditory stimuli. The order of touches in the sequence was free for the groups with freedom in response choice and determined for the yoked groups. A perceptual-motor change in the task was introduced in the adaptation phase. The experiment 1 was conducted to investigate the effect of freedom in response choice on the adaptive process in motor learning. Results showed that freedom in response choice during the stabilization phase benefited adaptive process. The experiment 2 was conducted to investigate the effect of learning goal both on the learner\'s choice and on the adaptive process in motor learning. Results indicated that learning goal had an effect on learners\' choices, but these choices did not lead to superiority in performance measures during the adaptive phase. The results also showed less time for planning the action in the first block of adaptive phase, suggesting better preparation for a new situation in the learning goal condition. Experiments 3 and 4 were conduced to investigate the effect of response variability resulting from freedom in response choice with learning goal on the adaptive process in motor learning. Results of both experiments revealed that, with learning goal, when freedom in response choice is actively and effectively explored, performance in the adaptation phase is favored, with indicative of superiority of higher sequence variations condition over the higher number of sequences used condition in the stabilization phase. Experiments 5 to 8 were conduced to compare the effect of variability resulting from freedom in response choice, with learning goal, to the effect of externally determined variability on the adaptive process in motor learning. The results of these experiments indicated that freedom in response choice is not enough to benefit adaptive process. When response variability resulting from freedom was lower, the benefits were absent, but when it was higher, the benefits were matched to those of the externally determined response variability

The primary purpose of this study was to examine whether variability of practice enhances neuromuscular adaptations when compared to traditional strength training. The secondary purpose was to investigate whether there was a difference in perception of exertion between the two strength programs. Forty one subjects (23 women and 18 men) were assigned to either the control group or one of two treatment groups by a blocked-random method. Subject's one repetition maximum (1RM) for the kettlebell press and leg press were measured at baseline, after 4 weeks of training, and after 8 weeks of training. The treatment groups completed 8 weeks of training consisting of 3 days a week with at least one recovery day in between each session. In weeks 1 through 3, subjects undergoing the traditional treatment completed 3 sets of 8 repetitions at 70% of their 1RM for each exercise. Weeks 4 through 6 were composed of 3 sets of 6 repetitions at 77% 1RM. In weeks 7 and 8, 3 sets of 4 repetitions at 85% 1RM were performed. Over the course of the eight weeks, the variable treatment was comprised of 5 sets of the kettlebell and leg press. A set of 4 repetitions at 77% of the subject's 1RM, one of 5 repetitions at 70% 1RM, another of 3 repetitions at 85% 1RM, one of 6 repetitions at 65% 1RM, and finally a set of 2 repetitions at 93% 1RM were performed every session. The order of these sets were changed every 3 weeks, altering where in the session the highest intensity set was in relation to the lower intensity sets. Ratings of perceived exertion (RPE) were recorded following treatment to determine subject's perception of intensity during each set. Analysis of variance with repeated measures did not reveal significantly different strength gains between treatment groups in either lift, although variable treatment resulted in greater mean strength gains over almost every time interval. Analyses of RPE data revealed significantly lower reported RPE values for the variable treatment compared to the traditional treatment in both lifts. The greater mean strength gains and significantly lower RPEs of the variable treatment program compel us to conclude it is a superior training method for increasing strength compared to the traditional program.