Estimation of Maximal Lactate Steady State Using the Sweat Lactate Sensor

doi:10.21203/rs.3.pex-2321/v1

Method Article

Estimation of Maximal Lactate Steady State Using the Sweat Lactate Sensor

https://doi.org/10.21203/rs.3.pex-2321/v1

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A simple, non-invasive algorithm for maximal lactate steady state (MLSS) assessment has not been developed. We examined whether MLSS can be estimated from the sweat lactate threshold (sLT) using a novel sweat lactate sensor for healthy adults, with consideration of their exercise habits. Fifteen adults representing diverse fitness levels were recruited. Participants with/without exercise habits were defined as trained/untrained, respectively. Constant-load testing for 30 min at 110%, 115%, 120%, and 125% of sLT intensity was performed to determine MLSS. The MLSS based on sLT was higher in the trained group as compared to the untrained group. A total of 80% of trained participants had an MLSS of 120% or higher, while 75% of untrained participants had an MLSS of 115% or lower based on sLT. MLSS was successfully estimated using sLT, with 120% or more in trained participants and 115% or less in untrained participants.

Sweat lactate sensor

Maximal lactate steady state

Exercise habit

・Grace Imaging Inc., Tokyo, Japan,

・Aeromonitor, AE-301S, Minato Medical Science Co., Ltd., Osaka, Japan, 219AGBZX00095000

・StrengthErgo8 V2, Fukuda Denshi Co., Ltd, Tokyo, Japan, 21900BZX00988000

・POLAR H10 N, Polar Electro Japan, Tokyo, Japan, ‎92075964

・NIRO-200NX, Hamamatsu Photonics K.K, Hamamatsu, Japan, 221AFBZX00122000

・Lactate Pro 2, ARKRAY Inc., Kyoto, Japan, 25B1X00001000037

A flowchart of the study protocol is shown in Figure 1. First, the Ramp stress test was performed using an electromagnetically braked ergometer (StrengthErgo8 V2; Fukuda Denshi Co., Ltd., Tokyo, Japan) with a sweat lactate sensor (Grace Imaging Inc., Tokyo, Japan), an exhaled gas analyzer (Aeromonitor AE-301S; Minato Medical Science Co., Ltd., Osaka, Japan), and a heart rate (HR) monitor (POLAR H10 N; Polar Electro Japan, Tokyo, Japan). Subsequently, constant-load exercise was performed for 30 min at 125%, 120%, 115%, and 110% of sLT intensity in this order. An electromagnetically-braked ergometer was used during the exercise to determine MLSS ¹ . At least 24 hours were allowed between each test (mean: 7.0 ± 2.9 days) ² . During constant-load exercise, an exhaled gas analyzer, HR monitor, and near-infrared spectroscopy (NIRS) monitor (NIRO-200NX; Hamamatsu Photonics K.K., Hamamatsu, Japan) were attached. Blood lactate values were obtained via auricular pricking and gentle squeezing of the ear lobe using a blood lactate analyzer (Lactate Pro 2, ARKRAY Inc., Kyoto, Japan). Blood lactate levels were measured before exercise and every 5 min during exercise.

The study protocol was approved by the Institutional Review Board of the Keio University School of Medicine (approval number: 20190229) and conducted in accordance with the principles of the Declaration of Helsinki.

sLT determination

After calibration using saline for 2 or 3 min, the sensor chip connected to the sensor device was attached to the superior right upper limb of the participant ³ ⁴ , which was cleaned with an alcohol-free cloth. The upper arm has a high-sweat rate during physical excursions ⁵ . In addition, it is a site that does not interfere with exercise during pedaling tasks. Additionally, data were recorded at a 1-Hz sampling frequency for mobile applications with a Bluetooth connection. Recorded data were converted to moving average values over 13-s intervals and individually underwent zero correction using the baseline value. sLT was defined as the first significant increase in sweat lactate concentration above baseline based on a graphical plot (Figure 2)

MLSS determination

Blood lactate was measured before exercise and every 5 min during constant-load exercise for 30 min at 110%, 115%, 120%, and 125% of sLT intensity. The rotational speed was set at 70 rpm. The criteria that did not achieve the exercise and exceeded the MLSS included participants who could not finish the trial due to fatigue, but could not maintain bicycle pedaling at 70 rpm, as well as participants who could finish 30 minutes of exercise but had an increase in blood lactate of more than 1 mM from 10 min after exercise initiation to the end of the exercise. MLSS was defined as the greatest load among the loads in which blood lactate values at the end of exercise (30 min) increased within 1 mM, compared to those at 10 min after exercise initiation ¹ (Figure 3)

The sweat lactate sensor is not working properly.

・This device may have difficulty measuring when there is too little sweating. Especially when targeting older individuals, who may have less sweating, the sensor should be placed on the forehead or external environmental conditions during measurement should be adjusted to be hotter and more humid to stimulate sweating.

・This device may have a lower response to sweat lactate when the skin temperature is low ( 25℃). Therefore, the measurement site (upper arm or forehead) should not be cooled by air conditioning or other means.

1. Urhausen, A., Coen, B., Weiler, B. & Kindermann, W. Individual anaerobic threshold and maximum lactate steady state. Int J Sports Med. 14(3), 134-139 (1993).

2. Greco, C. C., Barbosa, L. F., Carita, R. A. & Denadai, B. S. Is maximal lactate steady state during intermittent cycling different for active compared with passive recovery? Appl Physiol Nutr Metab. 37, 1147-1152 (2012).

3. Seki, Y. et al. A novel device for detecting anaerobic threshold using sweat lactate during exercise. Sci Rep. 11, 4929 (2021).

4. Maeda, Y. et al. Implications of the Onset of Sweating on the Sweat Lactate Threshold. sensors. 23, 3378 (2023).

5. Havenith, G., Fogarty, A., Bartlett, R., Smith, C. J. & Ventenat, V. Male and female upper body sweat distribution during running measured with technical absorbents. European Journal of Applied Physiology. 104, 245-255 (2008).

6. Bull, F. C. et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine. 54, 1451-1462 (2020).

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Estimation of Maximal Lactate Steady State Using the Sweat Lactate Sensor

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