Prediction of oxygen uptake (VO2) using neural networks

This thesis focuses on using neural network models for the prediction of oxygen uptake (VO2). The predictions are made using regression techniques. The dataset contains independent predictor variables such as heart rate (HR), energy expenditure (EE), height, body mass, gender and age. VO2 is the output dependent variable. The goal is to evaluate and compare the performance of neural networks to other machine learning techniques such as support vector machines and multiple linear regression. Few neural network models have been tested previously in the literature for maximal oxygen uptake (VO2max) prediction. During the last decade, most approaches have focused on support vector machines and linear regression equations. In this thesis, data collected at the University of Jyväskylä is used to create a dataset for the prediction of VO2. A detailed statistical analysis has been performed to see the relationship between speed, VO2 and energy expenditure. Using 8 different combinations of predictor variables, neural network’s performance and the effect of predictor variables on the performance is measured. Data pre-processing is performed. R2 value and root mean square error value is used for measuring the performance of the machine learning models. Same data set is used for all models to ensure accurate results. The results of this thesis show that speed, VO2 and energy expenditure have a direct relationship. Males show higher energy produced as compared to females. The neural network model outperformed support vector machine and multiple linear regression by resulting in accurate predictions, high R2 value and low root mean square value. The highest accuracy is achieved with the model containing all predictor variables. The inclusion of HR as a predictor variable is important due to its effect on the performance of the model. Further advancements in neural networks can allow more accurate VO2 predictions, the model can also be used in a wearable device for real-time VO2 prediction. The same approach can be extended to predict VO2max values

Machine learning to model health with multimodal mobile sensor data

The widespread adoption of smartphones and wearables has led to the accumulation of rich datasets, which could aid the understanding of behavior and health in unprecedented detail. At the same time, machine learning and specifically deep learning have reached impressive performance in a variety of prediction tasks, but their use on time-series data appears challenging. Existing models struggle to learn from this unique type of data due to noise, sparsity, long-tailed distributions of behaviors, lack of labels, and multimodality. This dissertation addresses these challenges by developing new models that leverage multi-task learning for accurate forecasting, multimodal fusion for improved population subtyping, and self-supervision for learning generalized representations. We apply our proposed methods to challenging real-world tasks of predicting mental health and cardio-respiratory fitness through sensor data. First, we study the relationship of passive data as collected from smartphones (movement and background audio) to momentary mood levels. Our new training pipeline, which combines different sensor data into a low-dimensional embedding and clusters longitudinal user trajectories as outcome, outperforms traditional approaches based solely on psychology questionnaires. Second, motivated by mood instability as a predictor of poor mental health, we propose encoder-decoder models for time-series forecasting which exploit the bi-modality of mood with multi-task learning. Next, motivated by the success of general-purpose models in vision and language tasks, we propose a self-supervised neural network ready-to-use as a feature extractor for wearable data. To this end, we set the heart rate responses as the supervisory signal for activity data, leveraging their underlying physiological relationship and show that the resulting task-agnostic embeddings can generalize in predicting structurally different downstream outcomes through transfer learning (e.g. BMI, age, energy expenditure), outperforming unsupervised autoencoders and biomarkers. Finally, acknowledging fitness as a strong predictor of overall health, which, however, can only be measured with expensive instruments (e.g., a VO2max test), we develop models that enable accurate prediction of fine-grained fitness levels with wearables in the present, and more importantly, its direction and magnitude almost a decade later. All proposed methods are evaluated on large longitudinal datasets with tens of thousands of participants in the wild. The models developed and the insights drawn in this dissertation provide evidence for a better understanding of high-dimensional behavioral and physiological data with implications for large-scale health and lifestyle monitoring.The Department of Computer Science and Technology at the University of Cambridge through the EPSRC through Grant DTP (EP/N509620/1), and the Embiricos Trust Scholarship of Jesus College Cambridg

VO2FITTING : a free and open-source software for modelling oxygen uptake kinetics in swimming and other exercise modalities

The assessment of oxygen uptake (VO2) kinetics is a valuable non-invasive way to evaluate cardiorespiratory and metabolic response to exercise. The aim of the study was to develop, describe and evaluate an online VO2 fitting tool (VO2FITTING) for dynamically editing, processing, filtering and modelling VO2 responses to exercise. VO2FITTING was developed in Shiny, a web application framework for R language. Validation VO2 datasets with both noisy and non-noisy data were developed and applied to widely-used models (n = 7) for describing different intensity transitions to verify concurrent validity. Subsequently, we then conducted an experiment with age-group swimmers as an example, illustrating how VO2FITTING can be used to model VO2 kinetics. Perfect fits were observed, and parameter estimates perfectly matched the known inputted values for all available models (standard error = 0; p < 0.001). The VO2FITTING is a valid, free and open-source software for characterizing VO2 kinetics in exercise, which was developed to help the research and performance analysis communities

Digital phenotyping through multimodal, unobtrusive sensing

The growing adoption of multimodal wearable and mobile devices, such as smartphones and wrist-worn watches has generated an increase in the collection of physiological and behavioural data at scale. This digital phenotyping data enables researchers to make inferences regarding users’ physical and mental health at scale, for the first time. However, translating this data into actionable insights requires computational approaches that turn unlabelled, multimodal time-series sensor data into validated measures that can be interpreted at scale. This thesis describes the derivation of novel computational methods that leverage digital phenotyping data from wearable devices in large-scale populations to infer physical behaviours. These methods combine insights from signal processing, data mining and machine learning alongside domain knowledge in physical activity and sleep epidemiology. First, the inference of sleeping windows in free-living conditions through a heart rate sensing approach is explored. This algorithm is particularly valuable in the absence of ground truth or sleep diaries given its simplicity, adaptability and capacity for personalization. I then explore multistage sleep classification through combined movement and cardiac wearable sensing and machine learning. Further, I demonstrate that postural changes detected through wrist accelerometers can inform habitual behaviours and are valuable complements to traditional, intensity-based physical activity metrics. I then leverage the concomitant responses of heart rate to physical activity that can be captured through multimodal wearable sensors through a self-supervised training task. The resulting embeddings from this task are shown to be useful for the downstream classification of demographic factors, BMI, energy expenditure and cardiorespiratory fitness. Finally, I describe a deep learning model for the adaptive inference of cardiorespiratory fitness (VO2max) using wearable data in free living conditions. I demonstrate the robustness of the model in a large UK population and show the models’ adaptability by evaluating its performance in a subset of the population with repeated measures ~6 years after the original recordings. Together, this work increases the potential of multimodal wearable and mobile sensors for physical activity and behavioural inferences in population studies. In particular, this thesis showcases the potential of using wearable devices to make valuable physical activity, sleep and fitness inferences in large cohort studies. Given the nature of the data collected and the fact that most of this data is currently generated by commercial providers and not research institutes, laying the foundations for responsible data governance and ethical use of these technologies will be critical to building trust and enabling the development of the field of digital phenotyping.I was funded by GlaxoSmithKline and the Engineering and Physical Sciences Research Council. I was also supported by the Alan Turing Institute through their Enrichment Scheme

Techniques Based on Adaptive Neuro-Fuzzy Inference Systems (ANFIS) for Estimating and Evaluating Physical Demands at Work Using Heart Rate

RÉSUMÉ : Malgré l'évolution rapide de la mécanisation dans les industries lourdes, les emplois physiquement exigeants qui nécessitent un effort humain excessif représentent encore une part importante dans de nombreuses industries (foresterie, construction, mines, etc.). Des études ont montré que les charges de travail excessives imposées aux travailleurs sont la principale cause de fatigue physique, ce qui a des effets négatifs sur les travailleurs, leur performance et la qualité du travail. Par conséquent, les chercheurs ont souligné l'importance de la conception optimale des tâches (à l'intérieur des compétences des travailleurs) afin de maintenir la sécurité, la santé et la productivité des travailleurs. Toutefois, cela ne peut être atteint sans comprendre (c'est-à-dire mesurer et évaluer) les exigences physiologiques du travail. À cet égard, les trois études comprises dans cette thèse présentent des approches pratiques pour estimer et évaluer la dépense énergétique (DE), exprimée en termes de consommation d'oxygène (VO2), au cours du travail réel. La première étude présente de nouvelles approches basées sur le système d'inférence neuro-flou adaptatif (ANFIS) pour l'estimation de la VO2 à partir des mesures de la fréquence cardiaque (FC). Cette étude comprend deux étapes auxquelles ont participé 35 individus en bonne santé. Dans un premier temps, deux modèles novateurs individuels ont été développés en se basant sur l’ANFIS et les méthodes analytiques. Ces modèles s'attaquent au problème de l'incertitude et de la non-linéarité entre la FC et la VO2. Dans un deuxième temps, un modèle général ANFIS qui ne requiert pas d'étalonnage individuel a été développé. Les trois modèles ont été testés en laboratoire et sur le terrain. La performance de chaque modèle a été évaluée et comparée aux VO2 mesurées et à deux méthodes d'estimation individuelles et traditionnelles de VO2 (étalonnage linéaire et Flex-HR). Les résultats ont indiqué la précision supérieure obtenue avec la modélisation ANFIS individualisée (EMQ = 1,0 à 2,8 ml/kg.min en laboratoire et sur le terrain, respectivement). Le modèle analytique a surpassé l'étalonnage linéaire traditionnel et les méthodes Flex-HR avec des données terrain. Les estimations du modèle général ANFIS de la VO2 ne différaient pas significativement des mesures réelles terrain VO2 (EMQ = 3,5 ml/kg.min). Avec sa facilité d'utilisation et son faible coût de mise en œuvre, le modèle général ANFIS montre du potentiel pour remplacer n'importe laquelle des méthodes traditionnelles individualisées pour l’estimation de la VO2 à partir de données recueillies sur le terrain. La deuxième étude présente un modèle de prédiction de la VO2 basé sur ANFIS qui est inspiré de la méthode Flex-HR. Des études ont montré que la méthode Flex-HR est une des méthodes les plus précises pour l'estimation de la VO2. Toutefois, cette méthode est basée sur quatre paramètres qui sont déterminés individuellement et par conséquent ceci est considéré comme coûteux, chronophage et souvent peu pratique, surtout lorsque le nombre de travailleurs augmente. Le modèle prédictif proposé se compose de trois modules ANFIS pour estimer les paramètres de Flex-HR. Pour chaque module ANFIS, la sélection de variables d'entrée et le modèle d'évaluation ont été simultanément réalisés à l'aide de la combinaison de la technique de division des données en trois parties et la technique de validation croisée. La performance de chaque module ANFIS a été testée et comparée avec les paramètres observés ainsi qu'avec les modèles de Rennie et coll. (2001) à l'aide de données de test indépendant. En outre, les performances du modèle global de prédiction ANFIS dans l'estimation de la VO2 a été testé et comparé avec les valeurs mesurées de la VO2, la méthode de Flex-HR standard ainsi qu'avec les autres modèles généraux (c.-à-d., les modèles de Rennie et coll. (2001) et de Keytel et coll. (2005)). Les résultats n'ont indiqué aucune différence significative entre les paramètres observés et estimés de Flex-HR et entre la VO2 mesurée et estimée dans la plage de fréquence cardiaque globale et séparément dans différentes gammes de FC. Le modèle de prédiction ANFIS (EMA = 3 ml/kg.min) a montré de meilleures performances que les modèles de Rennie et coll. (EMA = 7 ml/kg.min) et les modèles de Keytel et coll. (EMA = 6 ml/kg.min) et des performances comparables avec la méthode standard de Flex-HR (EMA = 2,3 ml/kg.min) tout au long de la plage de fréquence cardiaque. Le modèle ANFIS fournit ainsi aux praticiens une méthode pratique, économique et rapide pour l'estimation de la VO2 sans besoin d'étalonnage individuel. La troisième étude présente une nouvelle approche basée sur l'ANFIS pour classer les travaux en quatre classes d'intensité (c'est-à-dire, très léger, léger, modéré et lourd) à l'aide du monitorage du rythme cardiaque. La variabilité intra-individuelle (différences physiologiques et physiques) a été examinée. Vingt-huit participants ont effectué le test de la montée des marches Meyer et Flenghi (1995) et le test maximal sur le tapis roulant pendant lesquels la fréquence cardiaque et la consommation d'oxygène ont été mesurées. Les résultats ont indiqué que le monitorage du rythme cardiaque (FC, FC max et FC repos) et du poids corporel sont des variables significatives pour classer le rythme de travail. Le classificateur ANFIS a montré une sensibilité, une spécificité et une exactitude supérieures par rapport à la pratique courante à l'aide de catégories de rythme de travail basées sur le pourcentage de fréquence cardiaque de réserve (% FCR), avec une différence globale de 29,6 % dans la précision de classification entre les deux méthodes et un bon équilibre entre la sensibilité (90,7 %, en moyenne) et la spécificité (95,2 %, en moyenne). Avec sa facilité de mise en œuvre et sa mesure variable, le classificateur ANFIS montre un potentiel pour une utilisation généralisée par les praticiens pour évaluation du rythme de travail.----------ABSTRACT : Despite the rapid evolution of mechanization in heavy industries, physically demanding jobs that require excessive human effort still represent a significant part of many industries (e.g., forestry, construction, mining etc.). Studies have shown that excessive workloads placed on workers are the main cause of physical fatigue, which has negative effects on the workers, their performance and quality of work. Therefore, researchers have emphasized on the importance of the optimal job design (within workers’ capacity) in order to maintain workers’ safety, health and productivity. However, this cannot be achieved without understanding (i.e., measuring and evaluating) the physiological demands of work. In this respect, the three studies comprising this dissertation present practical approaches for estimating and evaluating energy expenditure (EE), expressed in terms of oxygen consumption (VO2), during actual work. The first study presents new approaches based on adaptive neuro-fuzzy inference system (ANFIS) for the estimation of VO2 from heart rate (HR) measurements. This study comprises two stages in which 35 healthy individuals participated. In the first stage, two novel individual models were developed based on the ANFIS and the analytical methods. These models tackle the problem of uncertainty and nonlinearity between HR and VO2. In the second stage, a General ANFIS model was developed which does not require individual calibration. The three models were tested under laboratory and field conditions. Performance of each model was evaluated and compared to the measured VO2 and two traditional individual VO2 estimation methods (linear calibration and Flex-HR). Results indicated the superior precision achieved with individualized ANFIS modeling (RMSE= 1.0 and 2.8 ml/kg.min in laboratory and field, respectively). The analytical model outperformed the traditional linear calibration and Flex-HR methods with field data. The General ANFIS model’s estimates of VO2 were not significantly different from actual field VO2 measurements (RMSE= 3.5 ml/kg.min). With its ease of use and low implementation cost, the General ANFIS model shows potential to replace any of the traditional individualized methods for VO2 estimation from HR data collected in the field. The second study presents an ANFIS-based VO2 prediction model that is inspired by the Flex-HR method. Studies have shown that the Flex-HR method is one of the most accurate methods for VO2 estimation. However, this method is based on four parameters that are determined individually and therefore it is considered costly, time consuming and often impractical, especially when the number of workers increases. The proposed prediction model consists of three ANFIS modules for estimating the Flex-HR parameters. For each ANFIS module, input variables selection and model assessment were simultaneously performed using the combination of three-way data split and cross-validation techniques. The performance of each ANFIS module was tested and compared with the observed parameters as well as with Rennie et al.’s (2001) models using independent test data. In addition, the performance of the overall ANFIS prediction model in estimating VO2 was tested and compared with the measured VO2 values, the standard Flex-HR method as well as with other general models (i.e., Rennie et al.’s (2001) and Keytel et al.’s (2005) models). Results indicated no significant difference between observed and estimated Flex-HR parameters and between measured and estimated VO2 in the overall HR range, and separately in different HR ranges. The ANFIS prediction model (MAE = 3 ml/kg.min) demonstrated better performance than Rennie et al.’s (MAE = 7 ml/kg.min) and Keytel et al.’s (MAE = 6 ml/kg.min) models, and comparable performance with the standard Flex-HR method (MAE = 2.3 ml/kg.min) throughout the HR range. The ANFIS model thus provides practitioners with a practical, cost- and time-efficient method for VO2 estimation without the need for individual calibration. The third study presents a new approach based ANFIS for classifying work intensity into four classes (i.e., very light, light, moderate and heavy) by using heart rate monitoring. Intersubject variability (physiological and physical differences) was considered. Twenty-eight participants performed Meyer and Flenghi (1995) step-test and a maximal treadmill test, during which heart rate and oxygen consumption were measured. Results indicated that heart rate monitoring (HR, HRmax, and HRrest) and body weight are significant variables for classifying work rate. The ANFIS classifier showed superior sensitivity, specificity, and accuracy compared to current practice using established work rate categories based on percent heart rate reserve (%HRR), with an overall 29.6% difference in classification accuracy between the two methods, and good balance between sensitivity (90.7%, on average) and specificity (95.2%, on average). With its ease of implementation and variable measurement, the ANFIS classifier shows potential for widespread use by practitioners for work rate assessment

Muscle activation patterns in shoulder impingement patients

Introduction: Shoulder impingement is one of the most common presentations of shoulder joint problems 1. It appears to be caused by a reduction in the sub-acromial space as the humerus abducts between 60o -120o – the 'painful arc'. Structures between the humeral head and the acromion are thus pinched causing pain and further pathology 2. Shoulder muscle activity can influence this joint space but it is unclear whether this is a cause or effect in impingement patients. This study aimed to observe muscle activation patterns in normal and impingement shoulder patients and determine if there were any significant differences. Method: 19 adult subjects were asked to perform shoulder abduction in their symptomatic arm and non-symptomatic. 10 of these subjects (age 47.9 ± 11.2) were screened for shoulder impingement, and 9 subjects (age 38.9 ± 14.3) had no history of shoulder pathology. Surface EMG was used to collect data for 6 shoulder muscles (Upper, middle and lower trapezius, serratus anterior, infraspinatus, middle deltoids) which was then filtered and fully rectified. Subjects performed 3 smooth unilateral abduction movements at a cadence of 16 beats of a metronome set at 60bpm, and the mean of their results was recorded. T-tests were used to indicate any statistical significance in the data sets. Significance was set at P<0.05. Results: There was a significant difference in muscle activation with serratus anterior in particular showing a very low level of activation throughout the range when compared to normal shoulder activation patterns (<30%). Middle deltoid recruitment was significantly reduced between 60-90o in the impingement group (30:58%).Trends were noted in other muscles with upper trapezius and infraspinatus activating more rapidly and erratically (63:25%; 60:27% respectively), and lower trapezius with less recruitment (13:30%) in the patient group, although these did not quite reach significance. Conclusion: There appears to be some interesting alterations in muscle recruitment patterns in impingement shoulder patients when compared against their own unaffected shoulders and the control group. In particular changes in scapula control (serratus anterior and trapezius) and lateral rotation (infraspinatus), which have direct influence on the sub-acromial space, should be noted. It is still not clear whether these alterations are causative or reactionary, but this finding gives a clear indication to the importance of addressing muscle reeducation as part of a rehabilitation programme in shoulder impingement patients