Making sense of nanotechnology and training biometrics

Let’s face it, triathletes are besotted by and embracing of, the rapidly expanding world of nanotechnology and performance. Given the demands and complexity of the sport, and commitment required, it’s not surprising that the modern triathlon warrior expresses more than a passing interest to advances in materials and devices that can potentially contribute to shaving chunks off your PB. Stronger but lighter and aero-advanced bikes; lighter and more supportive footwear; reduced resistance swimwear; lighter yet functional apparel; and wearable biometric technology that can seemingly draw data on every conceivable physiological parameter.

Inventors of wearable nanotechnology invariably draw inspiration and parallels from traditional high precision, gold standard physiology laboratory metrics. Take the laboratory based VO2max test for example. In the 1920s, English physiologist A.V Hill, a Nobel prize winner from Cambridge University, demonstrated that oxygen uptake increased linearly with running speed. Since then, while a number of these early fundamentals still hold true, the equipment, methodology and interpretation of oxygen uptake kinetics has evolved considerably over many decades. For the uninitiated, VO2max (maximal rate of oxygen consumed and delivered to working muscles) is the gold standard evaluation of aerobic fitness.

From a healthcare perspective, a number of exquisite longitudinal studies have shown that VO2max is a powerful predictor of longevity. Indeed, a study by Laukkanen and colleagues (2004) demonstrated that for individuals with or without common risk factors, every 3.5ml.kg.min increase in VO2max (a relatively small rise for individuals with below average or average fitness) contributes to an average decrease of 17–29% in non-fatal and 28–51% in fatal cardiac events, after adjustment for age.

The rationale and outcomes for evaluating VO2max in athletes are numerous. Firstly, we can establish baseline reference points in a controlled environment, in order to monitor specific training and lifestyle responses and adaptations over time. Secondly, we can assist athletes and their coaches with making practical sense of training zones according to sub-maximal and maximal oxygen uptake, and other metabolic metrics evaluated within the same test. Thirdly, we can identify where the most likely improvements can be made (including metabolic economy, energy demands et al.), and predict performance outcomes. Last but not least, data acquired during subsequent VO2max tests can help us identify maladaptation in response to overtraining or illness. While it is possible to analyse oxygen uptake in a field setting, the equipment required is prohibitively complex and expensive for most.

Heart rate increases linearly with oxygen consumption, and can thus provide an indirect guide to metabolic and cardiovascular demand. Subsequently, athletes and coaches have utilised heart rate metrics in the field for some decades, as a performance monitoring tool. Since heart rate guidelines have limitations (e.g., heart rate is variable, affected by emotion, environment, nutrition, medication, training period, recovery status – to name a few), technologists have been prompted to explore the possibilities of measuring oxygen uptake in the field, via lightweight and affordable nanotechnology.

Numerous so-called “smart fabrics” have been recently developed to monitor a broad range of biometrics (heart rate variability, respiration, movement patterns, heart rhythm, ventilation, sleep patterns et al.). Hexoskin (hexoskin.com) is one such brand featuring a fitted smart shirt embedded with biometric nanotechnology. According to its website, Hexoskin claims to measure VO2max – along with a range of other respiratory, cardiac and movement metrics. Beltrame and Hughson (2017) conducted a study to validate the merit of applying wearable technology (Hexoskin) for analysis of pulmonary oxygen uptake (VO2) dynamics and subsequent aerobic responses during a pseudorandom ternary sequence (PRTS) over-ground walking protocol. Eight moderately trained adults (VO2max ~40ml.kg.min) wore the Hexoskin smart shirt, with accelerometers at the hip, during a range of walking and cycling activities, evaluating the magnitude of input changes delivered to the aerobic system. In essence, the PRTS over-ground walking protocol could evaluate aerobic system dynamics via simultaneous measurement of VO2 (metabolic system) and hip acceleration (Hexoskin). However, this research design has its limitations. Firstly, it should be noted that VO2 is not technically measured by the Hexoskin smartshirt. Rather, the Hexoskin software estimates VO2 via an algorithm that combines accelerometer movement inputs and simultaneous oxygen uptake measured via a portable metabolic system. Secondly, while hip accelerometer signals successfully validated the walking speed and metabolic demand relationship, the current algorithm used to estimate walking cadence (and therefore walking speed), may fail to identify steps during more complex body movements. Thirdly, the accelerometer input and aerobic dynamics relationship beyond walking speeds were not evaluated, therefore the application to athlete monitoring at high physical work rates is currently unknown.

Another study by Beltrame and colleagues (2017) investigated the efficacy of Hexoskin derived work rates and predicted VO2 during activities of daily living (ADL). VO2 temporal dynamics were evaluated via mean normalised gain amplitude (MNG). Sixteen healthy adults completed PRTS over-ground walking protocols similarly described in the first study. In essence, the predicted VO2 during ADL was strongly correlated (r = 0.87, P < 0.001) with the measured VO2. In keeping with the limitations of the first study, the exercise protocols were typical of daily living activities, and therefore only light-moderate when considering absolute metabolic demands. As the authors rightly conclude in their manuscript, future studies proposing to apply the “sub-maximal” algorithm to high-intensity activities must recognise that VO2 dynamics become more complex with the potential for nonlinear contributions, and therefore reliability questions.

Humon Hex (humon.io) is a new kid on the sports nanotechnology block, with a device that straps around the thigh during exercise, using near-infrared spectroscopy to measure haemoglobin saturation in muscles (SmO2). LEDs emit light into the surrounding tissue, with detectors measuring subsequent light intensity that penetrates muscle; connecting to your smartphone or Garmin via Bluetooth. The Humon Hex website claims that the device “helps endurance athletes train smarter by monitoring the way their muscles are using oxygen in real time, and empowering them with the information they need to know when and how hard to push themselves”. At the time of writing this editorial (July 2017), Humon Hex were literally at a stage of launching the product and taking pre-orders. No specific validation publications were available on their website, and when communicating with the company seeking product efficacy, yours truly was informed that a recently completed manuscript was being prepared for submission to a peer-reviewed journal. We shall wait with baited breath. Without scientific evidence, the product efficacy and reliability is currently unknown. That said, the rationale of near-infrared spectroscopy to assess SmO2 during exercise, and in response to a variety of training interventions has been tested in a number of scientifically controlled environments, and is certainly a novel approach to performance monitoring when considering a typically tight relationship between SmO2 and VO2 during the right circumstances. Yes, that does mean variability is expected when skin blood flow and the rate of fluid shifts increase in muscle.

Considerations and take home message for triathletes

In principle, the application of wearable nanotechnology is supposed to make life for athletes more empowering, yet simpler and streamlined. One must not forget that biometrics do not answer questions or solve problems. They provide data in response to a series of actions. Ultimately, the human on the end of the device needs to make decisions about compliance to a training set, or whether a specific level of intensity in training or competition is sustainable. The greater the magnitude of data, more often then not you end up with more questions than answers. Therefore, when it comes to sifting through the myriad of technology options, you need to pick your poison carefully. Wearable technology as described here is invariably characterised by some level of uncertainty; although I will reserve conclusive judgement on the Humon Hex device until their first validation manuscript is made available. The logical approach is this: if there is persistent difficulty interpreting and applying data to your training and competition decisions, then it’s pointless (to you). As fast as biometric technology is progressing, nothing can replace your coach and/or sports scientist’s resourcefulness and experience when it comes to planning, monitoring and managing your performance needs.

PHOTOGRAPY BY Hexoskin and Humon Hex

References:

Laukkanen, JA., et al. (Eur Heart J, 2004). The predictive value of cardiorespiratory fitness for cardiovascular events in men with various risk profiles: a prospective population-based cohort study.

Beltrame, T and Hughson, R (Am J Physiol Regul Integr Comp Physiol, 2017). Aerobic system analysis based on oxygen uptake and hip acceleration during random over-ground walking activities.

Beltrame, T., et al. (Scientific Reports, 2017). Prediction of oxygen uptake dynamics by machine learning analysis of wearable sensors during activities of
daily living.

ABOUT THE AUTHOR

Simon Sostaric

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