About Sport and Exercise Analysis

Sport and exercise analysis features providing detailed performance analytics and heart rate recovery for different types of training and exercise sessions are described here. These features are available in selected Kubios HRV software products as follows:

Cardiorespiratory function

Cardiac function is represented by heart rate (HR), which is divided into zones with respect to person’s maximal heart rate (HRmax) or heart rate reserve (HRres). HRmax is the maximum heart rate that you reach during an incremental endurance test continued until exhaustion. Alternatively, you can exercise at your max pace (e.g., 3 x 3-4 min running blocks, 90-120 sec recovery between bouts) and add ~10% to the average HR during the bouts to estimate HRmax. Heart rate reserve, on the other hand, is the difference between your maximal HR and your resting HR, i.e. HRres = HRmax – HRrest. Instantaneous HR  and the time spent at each HR zone are reported as illustrated in Fig. 1.

Respiratory rate (RESP) is estimated from the HRV data using a validated algorithm [8], [16]. RESP is an important parameter in sport and exercise analysis since it is a strong marker of “physical effort”. Compared to oxygen consumption (VO2) and HR, RESP responds rapidly to fast changes in workload (characteristic especially for high intensity interval training, HIIT), and thus, RESP is strongly associated with the on/off metabolic demand [12]. Instantaneous RESP and the time spent at the three RESP zones (LIGHT: below 21 breaths/min; MODERATE: between 21-32 breaths/min; HARD: above 32 breaths/min ) are reported as illustrated in Fig. 1.

About Sport and Exercise AnalyticsFigure 1: Illustration of cardiorespiratory function. Heart rate and respiratory rate time trends (left) and zones (right)

Training effect

Training intensity and volume analysis in sport and exercise are commonly assessed using the training impulse (TRIMP), which is a rather commonly used index for training effect. The TRIMP is computed according to exponential Banister’s model [11], which is defined for male and females subjects as

    \begin{eqnarray*} \rm TRIMP &=& T \times \Delta HR \times 0.64 e^{1.92\times\Delta HR},\quad {\rm (Male)} \\ \rm TRIMP &=& T \times \Delta HR \times 0.86 e^{1.67\times\Delta HR},\quad {\rm (Female)} \end{eqnarray*}

where T is the duration of exercise and \rm\Delta HR=\frac{HR_{ex}-HR_{rest}}{HR_{max}-HR_{rest}} is a heart rate reserve ratio.TRIMP accumulation rate increases exponentially as a function of exercise intensity, modelling lactate accumulation during exercise. The TRIMP is computed using beat-to-beat HR values, and therefore, instantaneous value of TRIMP (TRIMP/min) can be reliably derived to represent training intensity. The accumulation of TRIMP (i.e., cumulative sum of TRIMP/min) reflects training load accumulation and is used as the primary index of training volume.

According to the instantaneous TRIMP (TRIMP/min) values, training intensity can be divided into five zones: VERY LIGHT (0-0.2 TRIMP/min), LIGHT (0.2-0.6 TRIMP/min), MODERATE (0.6-1.3 TRIMP/min), HARD (1.3-2.5 TRIMP/min), and MAXIMUM (2.5-4.5 TRIMP/min). Similarly, TRIMP accumulation can be used as a measure of training load. The training load is divided into five zones: VERY LIGHT (0-15 TRIMP), LIGHT (15-40 TRIMP), MODERATE (40-80 TRIMP), HARD (80-150 TRIMP), and MAXIMUM (150-270 TRIMP). Where, the maximum TRIMP accumulation of 270 would be reached if you exercise 60-mins at maximum intensity (4.5 TRIMP/min x 60 mins).

training intensity and load (TRIMP)

Instantaneous TRIMP (TRIMP/min) and TRIMP accumulation time trends and TRIMP zones are reported as illustrated in Fig. 2. The zones show the time spent at each intensity zone, the overall training load, and the average training intensity (average value of instantaneous TRIMP/min values).

Training intensity and volume

Figure 2: Illustration of training effect. Training intensity and volume time trends (left) and zones (right).

Metabolic profile

In exercise prescription, training efforts are typically separated into three intensity zones based on aerobic and anaerobic thresholds, which are generally defined by the first and second ventilatory or lactate thresholds.

Ventilatory thresholds (VT1 and VT2)

First and second ventilatory thresholds (VT1 and VT2) are of great importance in sport and exercise analysis. In Kubios HRV software products, VT1 and VT2 are estimated with a proprietary algorithm. Ventilatory threshold estimation is based on instantaneous values or heart rate (HR), respiratory rate (RESP), and fractal behavior of HRV measured by detrended fluctuation analysis (DFA) alpha1 parameter (DFA-α1).  The algorithm was developed by using maximal cycle ergometer test data from 230 individuals. Ventilatory thresholds can be derived from different types of exercise recordings (raw ECG or beat-to-beat RR interval or IBI data is required). The accuracy of the algorithm is -1.2 ± 10.7 bpm (mean ± SD) for the VT1 and -1.0 ± 6.7 bpm for the VT2 (white paper coming soon).

Alternatively, ventilatory thresholds may also be assessed based on DFA-α1 only. Detrended fluctuation analysis of HRV data is a measure of nonlinear correlation properties and has been considered as a proxy for organismic demands [17]. DFA-α1 has been observed to decline with high work rates and correlate with the first (HRVT1: DFA-α1=0.75) and second (HRVT2: DFA-α1=0.50) ventilatory/lactate thresholds [14], [15], [9].

The ventilatory thresholds may be utilized in exercise prescription and intensity distribution monitoring. Instantaneous value of the Kubios VT estimate and the time spent at the three zones (below VT1, between VT1 and VT2, and above VT2) are reported as illustrated in Fig. 3. The instantaneous value of the VT estimate is between 0-3. where value 1 corresponds to VT1 and value 2 corresponds to VT2.

 

Energy expenditure (EE) and oxygen uptake (VO2)

Heart rate based energy expenditure models, provide a reliable estimates of daily energy expenditure. In Kubios HRV software the energy expenditure is divided into: 1) basal metabolic rate (BMR) computed using the Mifflin-St Jeor equation[10] and 2) activity related energy expenditure (EE) computed using the Keytel’s formula[7]. The energy expenditure computations are based on heart rate, body weight, height and age. In Kubios HRV, we compute the EE using beat-to-beat HR values, and thus, the instantaneous EE (kcal/min) can be reliably derived. The instantaneous values of EE can be used to assess how energy expenditure is distributed throughout the day.

Oxygen consumption during exercise is estimated by using a well known relationship between the heart rate and oxygen consumption [1], [2]. To establish a subject specific model for the relationship between instantaneous HR and VO2, subject’s resting and maximum HR as well as subject’s maximal oxygen uptake (VO2max) are taken into account. If subject’s maximal oxygen uptake is not known, it will be estimated according to a formula proposed by Jones et al. [6]

    \begin{equation*} {\rm VO2max} = -4.31 + 4.6\times {\rm Height} - 0.62\times {\rm Sex} - 0.021\times {\rm Age} \end{equation*}

It should be noted that knowing subject’s true VO2max value (which is typically measured during a maximal cardiopulmonary exercise test) will increase the accuracy of VO2 estimation, specifically for well-trained individuals for whom the equation by Jones et al. may underestimate the VO2max value. For 95% of adults (all ages) the VO2max value is between 24-56 ml/kg/min for males and 19-47 ml/kg/min for females, with a decreasing trend as a function of age [13], [20].

Instantaneous VO2 value and time spent at different metabolic zones are reported as illustrated in Fig. 3.

ventilatory thresholds and oxygen uptake

Figure 3: Illustration of metabolic profile. Ventilatory threshold (VT) and oxygen uptake (VO2) time trends (left) and zones (right).

Heart rate recovery

Heart rate recovery (HRR) tells how much HR drops at specific time frames after exercise cessation. Similar to HRV, HRR has been linked with training status due to its association with the autonomic nervous system. Well trained athletes show faster HRR compared to untrained individuals. In addition, longitudinal studies have shown faster HRR with an improvement in training status after a training intervention [3], [5]. Therefore, HRR indexes may be used in sport and exercise analysis as an indication of cardiorespiratory fitness. In Kubios HRV software products, HRR is reported at 60s, 120s, and 300s increments. In addition, a fast 30s recovery (T30) within 0-40s after exercise cessation is reported

heart rate recovery sports analytics

Figure 4: Illustration of heart rate recovery. Heart rate recovery (HRR) at 60s, 120s and 300s increments as well as a fast 30s recovery (T30).

Frequently Asked Question (FAQ)

What are the key metrics used in sport and exercise analysis?

In sport and exercise analysis, key metrics traditionally include heart rate and training impulse (TRIMP), assessed both as a function of time and cumulatively over the entire training session. These metrics help quantify training intensity and volume, providing a foundation for evaluating an athlete’s workload and performance.

 

What is the added value of HRV analysis in optimizing training for athletes?

Heart rate variability analysis adds significant value by offering deeper insights into training intensity and athlete’s performance. HRV decreases as exercise intensity increases due to parasympathetic nervous activity withdrawal, thus providing insight into exercise intensity. HRV data can be used to evaluate ventilatory thresholds as well as respiratory rate, which helps in fine-tuning training plans to enhance performance and prevent overtraining by ensuring athletes train at optimal levels.

 

How to know your optimal training zones?

Optimal training zones are determined by analyzing physiological responses, such as heart rate and HRV, during various exercise intensities. These zones guide athletes in training at intensities that are appropriate for their current fitness levels and goals. Kubios software helps by providing ventilatory threshold estimates, which are calculated from HRV data that can be measured outside laboratory conditions, that define these zones, enabling athletes to train more effectively.

 

How accurate are the Kubios ventilatory thresholds?

The ventilatory thresholds (VT1 and VT2) estimated by Kubios are derived from physiological data, including heart rate with respect to athlete’s HR reserve, respiratory rate, and fractal behavior of HRV. The accuracy of the algorithm is -1.2 ± 10.7 bpm (mean ± SD) for the VT1 and -1.0 ± 6.7 bpm for the VT2.

References

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  2. Christensen CC, Frey HM, Foenstelien E, Aadland E, and Refsum HE. A critical evaluation of energy expenditure estimates based on individual O2 consumption/heart rate curves and average daily heart rate. Am J Clin Nutr, 37(3):468-472, 1983.
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