Characteristics and coupling of cardiac and locomotor rhythms during treadmill walking tasks

Studying the variability of physiological subsystems (e.g., cardiac and locomotor control systems) has been insightful in understanding how functional and dysfunctional patterns emerge within their behaviors. The coupling of these subsystems (termed cardiolocomotor coupling) is believed to be important to maintain healthy functioning in the diverse conditions in which individuals must operate. Aging and pathology result in alterations to both the patterns of individual systems, as well as to how those systems couple to each other. By examining cardiac and locomotor rhythms concurrently during treadmill walking, it is possible to ascertain how these two rhythms relate to each other in different populations (i.e., younger and older adults) and with varying task constraints (i.e., a gait synchronization task or fast walking task). The purpose of this research was to simultaneously document the characteristics of cardiac and gait rhythms in younger (18-35 yrs) and older (63-80 yrs) healthy adults while walking and to establish the extent to which changes in these systems are coupled when gait is constrained. This study consisted of two repeated-measures experiments that participants completed on two separate days. Both experiments consisted of three 15-minute phases. During the first (baseline) and third (retention) phases of both experiments, participants walked with no cues or specific instructions at their preferred walking speed. During the second phase, participants were asked to synchronize their step falls to the timing of a visual cue (experiment 1) or to walk at 125% of their preferred walking speed (experiment 2). Fifty-one healthy adults (26 older, 67.67±4.70 yrs, 1.72±0.09 m, 70.13±14.30 kg; 25 younger, 24.57±4.29 yrs, 1.76±0.09 m, 73.34±15.35 kg) participated in this study. Participants’ cardiac rhythms (R-R interval time series) and locomotor rhythms (stride interval, step width, and step length time series) were measured while walking on a treadmill. Characteristics of variability in cardiac and locomotor rhythms and the coupling between cardiac and gait rhythms were measured. Results revealed that younger and older healthy adults alter gait patterns similarly when presented with a gait synchronization or fast walking task and that these tasks also alter cardiac patterns. Likewise, both groups exhibited enhanced cardiolocomotor coupling when tasked with a step timing constraint or increased speed during treadmill walking. Combined, these findings suggest that walking tasks likely alter both locomotor and cardiac dynamics and the coupling of physiological subsystems could be insightful in understanding the diverse effects aging and pathology have on individuals

PRECOOLING AND RUNNING ECONOMY

Precooling, or a reduction in core temperature (Tc) has been demonstrated to be a potent enhancer of endurance running performance, however there is no known mechanism for this improvement. By holding the exercise workload constant, changes in variables such as running economy (RE), heart rate, and ventilation (VE) can be determined as a result of precooling. Improved running economy, or a reduced oxygen cost of a specific workload, is linked to improved exercise performance. Purpose: To determine the changes in flexibility, RE, heart rate, VE, and Tc during running at a constant workload following cool water immersion and to determine any sex-specific responses. Methods: Fourteen well-trained runners (8 males and 6 females) completed four treadmill runs at a sex-specific velocity (8.0 mph for females and 8.6 mph for males). The first two runs served as accommodation trials. The third and fourth runs were preceded by either cool water immersion (24.8oC) for 40 minutes or quiet sitting. Oxygen consumption, heart rate, Tc, VE, and flexibility were measured during both experimental trials. Results: Running economy did not change as a result of the precooling treatment, whereas Tc and heart rate were reduced by 0.4oC and 5 beats per minute, respectively. Minute ventilation was reduced in the female subjects only (1.4 liters/min). Sex differences were apparent in Tc, heart rate, VE, and flexibility response. Conclusion: While the precooling procedure was effective in reducing Tc and heart rate, RE did not change. Thus, improvements in RE cannot explain the dramatic enhancements of endurance running performance that often occur post-cooling. Differences between male and female subjects in response to precooling were identified, most notably in VE

Gait Changes During Exhaustive Running

Runners adopt altered gait patterns as they fatigue which may increase energy expenditure and susceptibility to certain overuse injuries. Previous investigations have described changes in muscle performance and kinematic gait variables resulting from running fatigue. The purpose of this investigation was to characterize changes in joint moment patterns that develop as runners fatigue in order to better understand the kinetic bases for kinematic fatigue effects. It was hypothesized that when fatigued, runners would demonstrate increases in stance time, peak stance phase knee flexion angle, peak knee extension moment, peak swing phase hip flexion moment, and hip extension and plantarflexion angular impulse generated during stance. Eight recreational rearfoot-striking runners (height = 170.0 ± 9.8 cm; mass = 69.6 ± 15.1 kg) ran on a force-instrumented treadmill at a velocity 5% slower than that of lactate threshold until volitional exhaustion. Force and motion data were collected each minute and analyzed at six evenly-spaced time points over the run duration. Of the six hypotheses, only stance time changed significantly (p = 0.004), increasing in a linear manner over the course of the run (r2 = 0.946). Of the remaining hypotheses, peak knee flexion (r2 = 0.899) and hip extension angular impulse (r2 = 0.608) followed increasing trends over the course of the run. Individual participants often demonstrated joint moment trends consistent with fatigue effects reported in the literature, despite inconclusive group results. High variability in individual responses underscores the complexity of gait adaptations used by distance runners as they fatigue

The Effect of Downhill Running Training on 200m and 2000m Running Performance

Downhill running as a method of training for improved running performance is an option which has rarely been explored. The purpose of this study was to explore the idea that downhill interval training may be an effective form of improving efficiency and thus, performance time, in 200m and 2000m level running by producing increases in both stride length (SL) and stride frequency (SF). To test this hypothesis, twelve fit male subjects were divided into two training groups, downhill (D) and level (L), matched on the basis of a 2000m time trial performance and VO2max. The dependant variables of time, SL and SF for both 200m and 2000m time trials were measured before and after a six week training program which consisted of an 8x300m interval session run twice per week. The L and D groups performed these intervals, on a grass surface, with a level and a 3.8% downhill grade, respectively. No significant improvements in performance or differences between the two groups were found for either criterion distance on any of the variables. Significant correlations, however, were found between increases in both SL and SF and decreases in both run times between pre- and post-training tests for both groups. Increases in SF were significantly correlated (r=0.918, p\u3c0.01) with improvements in 2000m run time in the D group. SF was also found to significantly correlate with 200m time, as was both SL and SF with 2000m run time. It was concluded that neither the D or L training program implemented in this study yielded significant improvements in 200m or 2000m run times. However, the results did imply that increasing both SL and SF may be factors in improving running performance. In addition, the results suggest that downhill running may be beneficial for enhancing middle distance (2000m) running performance, particularly in increasing SF

Anthropometric determinants of economical runners

Running economy is one of the most important factors in predicting performance in distance running, especially in elite runners. A substantial difference, (e.g.; 30-40%) in running economy can be seen even among elite runners. While economy has traditionally been tested at 240-268 m/min, these paces are slower than those of elite runners in competition. It was hypothesized that various anthropometric and flexibility variables, previously evaluated in the scientific literature, would more strongly correlated with running economy at speeds in excess of 268 m/min. Considering the link between elastic energy storage and return and the metabolic cost of running, variables that allow for increased storage might be correlated with enhanced running economy. In a group of nine well-trained male runners these variables were examined in relation to running economy measured as oxygen consumption in ml/kg/min during treadmill running at 268 m/min, 290 m/min, 310 m/min and 320 m/min. At 268 m/min, Achilles tendon moment arm and arch stiffness both displayed moderate correlations (r=0.69, p<.05) and (r=-0.673, p<.05), respectively) with oxygen consumption. Also, proportional leg length showed a strong negative correlation (r=-0.85, p<.05) with oxygen consumption at 320 m/min. In conclusion, the present study found smaller moment arms of the Achilles tendon, stiffer arches, and relative leg length to be related to reduced oxygen consumption while running at submaximal paces.Kinesiology and Health Educatio

Effects of synchronous, auditory stimuli on running performance and heart rate

Research has demonstrated that the human being tends to couple body movements and external, acoustic stimuli (metronome or music). This effect is called auditory-motor synchronization. Motivational music possesses qualities which distract from feelings like fatigue and exertion. Combining these two effects may enhance the sports performance even more. Investigations showed that runners can increase their original cadence up to 2%. The purpose of this study was to examine the effects of accelerated, synchronized stimuli on the running performance. Therefore, 28 students (15 ♀, 13 ♂) of the Institute of Sports Science in Innsbruck were asked to do two cooper tests each. After run 1 (no auditory signal), the sample was divided into two groups. In run 2, which took place on a different day, one group listened to music while running; the other group was stimulated by the sound of a metronome. Distance (m) and average heartrate were measured. 75% of the athletes achieved a greater distance under the influence of an acoustic stimulus. In fact, the running distance changed significantly using an acoustic stimulus: +61 m (SD ± 100) or 2.1% (SD ± 3.6). In group 1 (music), the performance improved up to + 3.8% (SD ± 3.3). This difference was significant compared to group 2 (metronome). The average heart rate decreased by 1.5 beats (SD ± 5) from run 1 to run 2. Influenced by music, the average heart rate measured 179 beats (SD ± 8) in contrast to 182 beats (SD ± 10) in run 1 (no acoustic stimulus). If the tempo of the acoustic stimulus is adapted to the accelerated cadence of an athlete (maximum 2%), improved distances due to the synchronization effect can be achieved. In combination with the motivating qualities of music, improved effects in sport performances could be produced

Sincronismo cardiolocomotor : interação entre parâmetros locomotores, neuromusculares e fisiológicos e sua repercussão sobre a bioenergética da corrida de longa distância

Introdução: O sincronismo cardiolocomotor (SCL) ocorre quando as frequências desses dois sistemas assumem um ritmo oscilatório comum e tem sido observado em atividades cíclicas. Porém, pouco se sabe sobre sua repercussão no desempenho esportivo. Dentre os possíveis efeitos do SCL destaca-se o aperfeiçoamento da função cardíaca e a consequente otimização da perfusão sanguínea nos músculos ativos, com redução no dispêndio energético do músculo cardíaco. Tais efeitos podem impactar positivamente a economia de corrida. Objetivo: Analisar as interações entre parâmetros locomotores, neuromusculares e fisiológicos, especialmente o SCL, e a repercussão dessas interações na bioenergética da corrida de longa distância. Métodos: Corredores de longa distância realizaram testes de corrida em esteira rolante, com duração entre três e cinco minutos cada, em diferentes velocidades. Sinais de eletrocardiografia (ECG) e eletromiografia de superfície (EMG) dos músculos vasto lateral e gastrocnêmio medial foram registrados para determinar o SCL por meio da Coerência Wavelet que retornou o Coeficiente de Coerência Wavelet (CCW) variando de 0 (ausência de coerência) até 1 (coerência perfeita), bem como as frequências de sincronização (Freq Sincro). Nós consideramos o SCL como manifesto quando o CCW > 0,8. Os parâmetros espaço-temporais da corrida foram obtidos por cinemetria e os parâmetros energéticos (custo de transporte) e hemodinâmicos (pulso de oxigênio) por análise de gases metabólicos Na análise estatística usou-se os Modelos Lineares Mistos Generalizados (GLMMs), com nível de significância de 5%. Resultados: Em todos os testes, observamos poucos eventos considerados como SCL, em média menos de 1% dos dados analisados, embora tenhamos observado de forma sistemática um componente de frequência (Fsincro) nos sinais centrado na frequência de passo, algo entre 160 a 170 passos min-1, que pode ser indicativo do arrastamento da frequência cardíaca pela frequência locomotora. As diferenças estatísticas encontradas nas variáveis hemodinâmicas e metabólicas não parecem ser consequência da SCL. Conclusão: Visto que o SCL não foi identificado nos nossos achados, a repercussão deste nas variáveis mecânicas, hemodinâmicas e metabólicas, incluindo a economia de corrida, são apenas especulativas.Introduction: Cardiolocomotor synchronization (CLS) occurs when the frequencies of these two systems assume a common oscillatory rhythm and has been observed in cyclic activities such, but little is known about its repercussion in sports performance. Among the possible effects of CLS are the improvement of cardiac function and the consequent optimization of blood perfusion in the muscles involved in the activity, with reduction of the energy expenditure of the cardiac muscle. Such effects may positively impact the running economy. Aims: To analyze the interactions between locomotor, neuromuscular and physiological parameters, especially cardiolocomotor synchrony, and the repercussion of these interactions on bioenergetics of long distance running. Methods: Long distance runners performed treadmill running tests, lasting between three and five minutes each, at different speeds. Electrocardiography (ECG) and surface electromyography (SEMG) of the vastus lateralis and medial gastrocnemius muscles signals were recorded to determine the CLS by Wavelet Coherence that returned the Wavelet Coherence Coefficient (WCC) ranging from 0 (no coherence) to 1 (perfect coherence), as well as the synchronization frequencies (Freq Synchro). We considered CLS as manifested when WCC > 0.8. The running spatiotemporal parameters were obtained by cinematic and the energetic (cost of transport) and hemodynamic (oxygen pulse) parameters by metabolic gases analysis. Statistical analysis was performed using Generalized Mixed Linear Models (GLMMs), with a significance level of 5%. Results: In all tests, we observed rarely events considered as CLS, on average less than 1% of the data analyzed, although we systematically observed a component of frequency (Freq Synchro) in the signals centered on the step frequency, something between 160 and 170 steps min-1, which may be indicative of the entrainment of the heart rate by the locomotor frequency. The statistical differences found in hemodynamic variables and metabolic variables do not seem to be a consequence of CLS. Conclusion: Since CLS was not identified in our findings, its repercussion on mechanical, hemodynamic and metabolic variables, including running economy, is just speculation