{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,22]],"date-time":"2026-09-22T03:17:14Z","timestamp":1790047034916,"version":"4.0.1"},"reference-count":50,"publisher":"MDPI AG","issue":"14","license":[{"start":{"date-parts":[[2025,7,18]],"date-time":"2025-07-18T00:00:00Z","timestamp":1752796800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"the Italian Ministry of Research through the WEPOP","award":["2022RKLB3J"],"award-info":[{"award-number":["2022RKLB3J"]}]},{"name":"the Italian Ministry of Research through the WEPOP","award":["PON R&I ARSO1_00345"],"award-info":[{"award-number":["PON R&I ARSO1_00345"]}]},{"name":"the Italian Ministry of Education, University and Research","award":["2022RKLB3J"],"award-info":[{"award-number":["2022RKLB3J"]}]},{"name":"the Italian Ministry of Education, University and Research","award":["PON R&I ARSO1_00345"],"award-info":[{"award-number":["PON R&I ARSO1_00345"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Photoplethysmographic (PPG) sensors are small and cheap wearable sensors which open the possibility of monitoring physiological parameters such as heart rate during normal daily routines, ultimately providing valuable information on health status. Despite their potential and distribution within wearable devices, their accuracy is affected by several influencing parameters, such as contact pressure and physical activity. In this study, the effect of contact pressure (i.e., at 20, 60, and 75 mmHg) and intensity of physical activity (i.e., at 3, 6, and 8 km\/h) were evaluated on a sample of 25 subjects using both a reference device (i.e., an electrocardiography-based device) and a PPG sensor applied to the skin with controlled contact pressure values. Results showed differing accuracy and precision when measuring the heart rate at different pressure levels, achieving the best performance at a contact pressure of 60 mmHg, with a mean absolute percentage error of between 3.36% and 6.83% depending on the physical activity levels, and a Pearson\u2019s correlation coefficient of between 0.81 and 0.95. Plus, considering the individual optimal contact pressure, measurement uncertainty significantly decreases at any contact pressure, for instance, decreasing from 15 bpm (at 60 mmHg) to 8 bpm when running at a speed of 6 km\/h (coverage factor k = 2). These results may constitute useful information for both users and manufacturers to improve the metrological performance of PPG sensors and expand their use in a clinical context.<\/jats:p>","DOI":"10.3390\/s25144477","type":"journal-article","created":{"date-parts":[[2025,7,18]],"date-time":"2025-07-18T11:12:34Z","timestamp":1752837154000},"page":"4477","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["Experimental Analysis on the Effect of Contact Pressure and Activity Level as Influencing Factors in PPG Sensor Performance"],"prefix":"10.3390","volume":"25","author":[{"given":"Francesco","family":"Scardulla","sequence":"first","affiliation":[{"name":"Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7982-208X","authenticated-orcid":false,"given":"Gloria","family":"Cosoli","sequence":"additional","affiliation":[{"name":"Department of Theorethical and Applied Sciences, eCampus University, v. Isimbardi 10, 22060 Novedrate, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Cosmina","family":"Gnoffo","sequence":"additional","affiliation":[{"name":"Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-5435-8516","authenticated-orcid":false,"given":"Luca","family":"Antognoli","sequence":"additional","affiliation":[{"name":"Department of Industrial Engineering and Mathematical Sciences, Marche Polytechnic University, v. Brecce Bianche 12, 60131 Ancona, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6177-442X","authenticated-orcid":false,"given":"Francesco","family":"Bongiorno","sequence":"additional","affiliation":[{"name":"Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0000-5303-5408","authenticated-orcid":false,"given":"Gianluca","family":"Diana","sequence":"additional","affiliation":[{"name":"Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4728-3736","authenticated-orcid":false,"given":"Lorenzo","family":"Scalise","sequence":"additional","affiliation":[{"name":"Department of Industrial Engineering and Mathematical Sciences, Marche Polytechnic University, v. Brecce Bianche 12, 60131 Ancona, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4837-1797","authenticated-orcid":false,"given":"Leonardo","family":"D\u2019Acquisto","sequence":"additional","affiliation":[{"name":"Department of Engineering, University of Palermo, Viale delle Scienze, Ed. 8, 90128 Palermo, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1700-3075","authenticated-orcid":false,"given":"Marco","family":"Arnesano","sequence":"additional","affiliation":[{"name":"Department of Theorethical and Applied Sciences, eCampus University, v. Isimbardi 10, 22060 Novedrate, Italy"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2025,7,18]]},"reference":[{"key":"ref_1","unstructured":"(2024, November 01). Life Expectancy and Healthy Life Expectancy. Available online: https:\/\/www.who.int\/data\/gho\/data\/themes\/mortality-and-global-health-estimates\/ghe-life-expectancy-and-healthy-life-expectancy."},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Maresova, P., Javanmardi, E., Barakovic, S., Barakovic Husic, J., Tomsone, S., Krejcar, O., and Kuca, K. (2019). Consequences of chronic diseases and other limitations associated with old age\u2014A scoping review. BMC Public Health, 19.","DOI":"10.1186\/s12889-019-7762-5"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"115","DOI":"10.1007\/s10916-017-0760-1","article-title":"A Systematic Review of Wearable Patient Monitoring Systems\u2014Current Challenges and Opportunities for Clinical Adoption","volume":"41","author":"Baig","year":"2017","journal-title":"J. Med. Syst."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"101600","DOI":"10.1016\/j.seps.2023.101600","article-title":"An analysis of the thematic evolution of ageing and healthcare expenditure using word embedding: A scoping review of policy implications","volume":"87","author":"Lopreite","year":"2023","journal-title":"Socioecon. Plann. Sci."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"113047","DOI":"10.1016\/j.measurement.2023.113047","article-title":"Enhancing personal comfort: A machine learning approach using physiological and environmental signals measurements","volume":"217","author":"Cosoli","year":"2023","journal-title":"Measurement"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"84","DOI":"10.1038\/s41746-023-00828-5","article-title":"Systematic review and meta-analysis of performance of wearable artificial intelligence in detecting and predicting depression","volume":"6","author":"AlSaad","year":"2023","journal-title":"NPJ Digit. Med."},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Liu, P., Song, Y., Yang, X., Li, D., and Khosravi, M. (2024). Medical intelligence using PPG signals and hybrid learning at the edge to detect fatigue in physical activities. Sci. Rep., 14.","DOI":"10.1038\/s41598-024-66839-8"},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Loh, H.W., Xu, S., Faust, O., Ooi, C.P., Barua, P.D., Chakraborty, S., Tan, R.S., Molinari, F., and Acharya, U.R. (2022). Application of photoplethysmography signals for healthcare systems: An in-depth review. Comput. Methods Programs Biomed., 216.","DOI":"10.1016\/j.cmpb.2022.106677"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"113150","DOI":"10.1016\/j.measurement.2023.113150","article-title":"Photoplethysmograhic sensors, potential and limitations: Is it time for regulation? A comprehensive review","volume":"218","author":"Scardulla","year":"2023","journal-title":"Measurement"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Almarshad, M.A., Saiful Islam, M., Al-Ahmadi, S., and BaHammam, A.S. (2022). Diagnostic Features and Potential Applications of PPG Signal in Healthcare: A Systematic Review. Healthcare, 10.","DOI":"10.3390\/healthcare10030547"},{"key":"ref_11","unstructured":"(2025, April 29). Are Your Home and Your Belongings Internet-Connected? Products Eurostat News-Eurostat. Available online: https:\/\/ec.europa.eu\/eurostat\/web\/products-eurostat-news\/-\/ddn-20210225-1."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"282","DOI":"10.3390\/electronics3020282","article-title":"Wearable Photoplethysmographic Sensors\u2014Past and Present","volume":"3","author":"Tamura","year":"2014","journal-title":"Electronics"},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Haque, C.A., Hossain, S., Kwon, T.H., and Kim, K.D. (2021, January 20\u201322). Comparison of Different Methods to Estimate Blood Oxygen Saturation using PPG. Proceedings of the 2021 International Conference on Information and Communication Technology Convergence (ICTC), Jeju Island, Republic of Korea.","DOI":"10.1109\/ICTC52510.2021.9621142"},{"key":"ref_14","first-page":"314","article-title":"Determining factors of pulse oximetry accuracy: A literature review","volume":"224","author":"Cabanas","year":"2024","journal-title":"Rev. Cl\u00ednica Espa\u00f1ola (Engl. Ed.)"},{"key":"ref_15","doi-asserted-by":"crossref","unstructured":"Man, P.K., Cheung, K.L., Sangsiri, N., Shek, W.J., Wong, K.L., Chin, J.W., Chan, T.T., and So, R.H.Y. (2022). Blood Pressure Measurement: From Cuff-Based to Contactless Monitoring. Healthcare, 10.","DOI":"10.3390\/healthcare10102113"},{"key":"ref_16","doi-asserted-by":"crossref","unstructured":"Kuwalek, P., Burlaga, B., Jesko, W., and Konieczka, P. (2021). Research on methods for detecting respiratory rate from photoplethysmographic signal. Biomed. Signal Process. Control, 66.","DOI":"10.1016\/j.bspc.2021.102483"},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Ferizoli, R., Karimpour, P., May, J.M., and Kyriacou, P.A. (2024). Arterial stiffness assessment using PPG feature extraction and significance testing in an in vitro cardiovascular system. Sci. Rep., 14.","DOI":"10.1038\/s41598-024-51395-y"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Afzali Arani, M.S., Costa, D.E., and Shihab, E. (2021). Human Activity Recognition: A Comparative Study to Assess the Contribution Level of Accelerometer, ECG, and PPG Signals. Sensors, 21.","DOI":"10.3390\/s21216997"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Cosoli, G., Antognoli, L., Veroli, V., and Scalise, L. (2022). Accuracy and Precision of Wearable Devices for Real-Time Monitoring of Swimming Athletes. Sensors, 22.","DOI":"10.3390\/s22134726"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"372","DOI":"10.1016\/j.autcon.2016.08.029","article-title":"Feasibility analysis of heart rate monitoring of construction workers using a photoplethysmography (PPG) sensor embedded in a wristband-type activity tracker","volume":"71","author":"Hwang","year":"2016","journal-title":"Autom. Constr."},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Scardulla, F., D\u2019Acquisto, L., Colombarini, R., Hu, S., Pasta, S., and Bellavia, D. (2020). A Study on the Effect of Contact Pressure during Physical Activity on Photoplethysmographic Heart Rate Measurements. Sensors, 20.","DOI":"10.3390\/s20185052"},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Sirki\u00e4, J.-P., Panula, T., and Kaisti, M. (2024). Investigating the impact of contact pressure on photoplethysmograms. Biomed. Eng. Adv., 7.","DOI":"10.1016\/j.bea.2024.100123"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Lambert Cause, J., Sol\u00e9 Morillo, \u00c1., Garc\u00eda-Naranjo, J.C., Stiens, J., and da Silva, B. (2024). The Impact of Contact Force on Signal Quality Indices in Photoplethysmography Measurements. Appl. Sci., 14.","DOI":"10.3390\/app14135704"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"136","DOI":"10.1109\/RBME.2021.3121476","article-title":"A Review of Wearable Multi-wavelength Photoplethysmography","volume":"16","author":"Ray","year":"2021","journal-title":"IEEE Rev. Biomed. Eng."},{"key":"ref_25","doi-asserted-by":"crossref","unstructured":"Yan, L., Hu, S., Alzahrani, A., Alharbi, S., and Blanos, P. (2017). A Multi-Wavelength Opto-Electronic Patch Sensor to Effectively Detect Physiological Changes against Human Skin Types. Biosensors, 7.","DOI":"10.3390\/bios7020022"},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Han, S., Roh, D., Park, J., and Shin, H. (2019). Design of Multi-Wavelength Optical Sensor Module for Depth-Dependent Photoplethysmography. Sensors, 19.","DOI":"10.3390\/s19245441"},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Krishnan, S., Arg\u00fcello-Prada, E.J., Ferney, J., and Garc\u00eda, C. (2024). Machine Learning Applied to Reference Signal-Less Detection of Motion Artifacts in Photoplethysmographic Signals: A Review. Sensors, 24.","DOI":"10.3390\/s24227193"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Pandey, R.K., and Chao, P.C.P. (November, January 31). A Low-Power 54 \u03bcW Adaptive Analog Front-End with Adaptive Intensity Control for an Organic PPG Sensor in Wearable Devices. Proceedings of the 2021 IEEE Sensors, Sydney, Australia.","DOI":"10.1109\/SENSORS47087.2021.9639665"},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Scardulla, F., Riggi, C., Diana, G., and D\u2019Acquisto, L. (2024, January 12\u201314). Preliminary Analisys on the Effect of Skin Temperature on Photoplethysmographic Signal. Proceedings of the 2024 IEEE International Workshop on Metrology for Living Environment, Chania, Greece.","DOI":"10.1109\/MetroLivEnv60384.2024.10615655"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"18","DOI":"10.1038\/s41746-020-0226-6","article-title":"Investigating sources of inaccuracy in wearable optical heart rate sensors","volume":"3","author":"Bent","year":"2020","journal-title":"Npj Digit. Med."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"102038","DOI":"10.1016\/j.mex.2023.102038","article-title":"Methods for the metrological characterization of wearable devices for the measurement of physiological signals: State of the art and future challenges","volume":"10","author":"Cosoli","year":"2023","journal-title":"MethodsX"},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Kaur, A., and Arora, A. (2019, January 5\u20136). A Review on Reliability, Security and Future Aspects of Photoplethysmography. Proceedings of the 2019 2nd International Conference on Intelligent Computing, Instrumentation and Control Technologies (ICICICT), Kannur, India.","DOI":"10.1109\/ICICICT46008.2019.8993119"},{"key":"ref_33","unstructured":"Consumer Technology Association (CTA) (2022, September 29). Physical Activity Monitoring for Heart Rate (ANSI\/CTA-2065). Available online: https:\/\/shop.cta.tech\/products\/physical-activity-monitoring-for-heart-rate."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"333","DOI":"10.2147\/VHRM.S468382","article-title":"Validating the Accuracy of Omron HEM-1026 (HCR-1901T2\/HCR-1902T2): Blood Pressure Monitoring Device at Home, According to the Universal Protocol","volume":"20","author":"Takahashi","year":"2024","journal-title":"Vasc. Health Risk Manag."},{"key":"ref_35","doi-asserted-by":"crossref","unstructured":"Romagnoli, S., Ripanti, F., Morettini, M., Burattini, L., and Sbrollini, A. (2023). Wearable and Portable Devices for Acquisition of Cardiac Signals while Practicing Sport: A Scoping Review. Sensors, 23.","DOI":"10.3390\/s23063350"},{"key":"ref_36","doi-asserted-by":"crossref","unstructured":"Mart\u00edn-Escudero, P., Cabanas, A.M., Dotor-Castilla, M.L., Galindo-Canales, M., Miguel-Tobal, F., Fern\u00e1ndez-P\u00e9rez, C., Fuentes-Ferrer, M., and Giannetti, R. (2023). Are Activity Wrist-Worn Devices Accurate for Determining Heart Rate during Intense Exercise?. Bioengineering, 10.","DOI":"10.3390\/bioengineering10020254"},{"key":"ref_37","doi-asserted-by":"crossref","unstructured":"Morresi, N., Casaccia, S., and Revel, G.M. (2021, January 23\u201325). Metrological characterization and signal processing of a wearable sensor for the measurement of heart rate variability. Proceedings of the 2021 IEEE International Symposium on Medical Measurements and Applications (MeMeA), Lausanne, Switzerland.","DOI":"10.1109\/MeMeA52024.2021.9478713"},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"728","DOI":"10.1007\/s11036-019-01323-6","article-title":"Detection and Removal of Motion Artifacts in PPG Signals","volume":"27","author":"Pollreisz","year":"2022","journal-title":"Mob. Netw. Appl."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"180076","DOI":"10.1038\/sdata.2018.76","article-title":"Analysis: An optimal filter for short photoplethysmogram signals","volume":"5","author":"Liang","year":"2018","journal-title":"Sci. Data"},{"key":"ref_40","unstructured":"Tan, L., and Jiang, J. (2018). Digital Signal Processing: Fundamentals and Applications, Academic Press."},{"key":"ref_41","doi-asserted-by":"crossref","unstructured":"Lapitan, D.G., Rogatkin, D.A., Molchanova, E.A., and Tarasov, A.P. (2024). Estimation of phase distortions of the photoplethysmographic signal in digital IIR filtering. Sci. Rep., 14.","DOI":"10.1038\/s41598-024-57297-3"},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"1091","DOI":"10.1038\/s41597-024-03950-5","article-title":"A ballistocardiogram dataset with reference sensor signals in long-term natural sleep environments","volume":"11","author":"Li","year":"2024","journal-title":"Sci. Data"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"379","DOI":"10.1002\/pmrj.12424","article-title":"won Accuracy of Wearable Devices for Measuring Heart Rate During Conventional and Nordic Walking","volume":"13","author":"Baek","year":"2021","journal-title":"PMR"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1855","DOI":"10.1097\/00005768-200111000-00009","article-title":"The aftereffects of dynamic exercise on ambulatory blood pressure","volume":"33","author":"Pescatello","year":"2001","journal-title":"Med. Sci. Sports Exerc."},{"key":"ref_45","doi-asserted-by":"crossref","unstructured":"De Fazio, R., Mastronardi, V.M., De Vittorio, M., and Visconti, P. (2023). Wearable Sensors and Smart Devices to Monitor Rehabilitation Parameters and Sports Performance: An Overview. Sensors, 23.","DOI":"10.3390\/s23041856"},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"101086","DOI":"10.1016\/j.measen.2024.101086","article-title":"Application of wearable devices based on artificial intelligence sensors in sports human health monitoring","volume":"33","author":"Yang","year":"2024","journal-title":"Meas. Sens."},{"key":"ref_47","doi-asserted-by":"crossref","unstructured":"Lambert Cause, J., Sol\u00e9 Morillo, \u00c1., da Silva, B., Garc\u00eda-Naranjo, J.C., and Stiens, J. (2024). Evaluating Vascular Depth-Dependent Changes in Multi-Wavelength PPG Signals Due to Contact Force. Sensors, 24.","DOI":"10.3390\/s24092692"},{"key":"ref_48","doi-asserted-by":"crossref","first-page":"430","DOI":"10.1016\/j.clindermatol.2019.07.010","article-title":"Skin typing: Fitzpatrick grading and others","volume":"37","author":"Gupta","year":"2019","journal-title":"Clin. Dermatol."},{"key":"ref_49","unstructured":"(2025, July 05). Regulation-536\/2014-EN-EUR-Lex. Available online: https:\/\/eur-lex.europa.eu\/eli\/reg\/2014\/536\/oj\/eng."},{"key":"ref_50","unstructured":"(2025, July 05). Directive-2001\/83-EN-EUR-Lex. Available online: https:\/\/eur-lex.europa.eu\/eli\/dir\/2001\/83\/oj\/eng."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/14\/4477\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,9]],"date-time":"2025-10-09T18:12:07Z","timestamp":1760033527000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/25\/14\/4477"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2025,7,18]]},"references-count":50,"journal-issue":{"issue":"14","published-online":{"date-parts":[[2025,7]]}},"alternative-id":["s25144477"],"URL":"https:\/\/doi.org\/10.3390\/s25144477","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2025,7,18]]}}}