Renata Lopes Kruger

Renata Lopes KrugerMITACS Elevate Postdoctoral Associate, Hotchkiss Brain Institute, Physiology and Pharmacology Department, Cumming School of Medicine, University of Calgary (Canada)

09/2015 - 08/2019 - Calgary, Canada

Effects of exercise on neuromuscular fatigue during dynamic muscle contractions in young and aging populations (Principal Supervisor - Cosupervisor: Dr Pierre Samozino)


Dr. Renata L. Krüger is a postdoctoral associate in the Hotchkiss Brain Institute at the University of Calgary. Her current research aims to investigate the impact of virtual reality exercise interventions on functional capacity, sleep quality, and cognition in older adults who live in seniors care homes. Her training is currently supported by a MITACS Elevate postdoctoral fellowship. In April 2020, she was awarded a postdoctoral fellowship from the Canadian Institutes of Health Research. In June 2020, Renata had published 22 peer-reviewed publications (9 as first author) and 22 conference abstracts. She had 4 manuscripts under review (1 as first author) and 3 in preparation (2 as first author).

Renata obtained her PhD degree in the Faculty of Kinesiology at the University of Calgary under the supervision of Prof. Guillaume Millet. The first aim of her PhD thesis was to compare dynamic measures of fatigue (dynamic torque, velocity, and power) with measures associated with maximal isometric force after different exercise intensities-durations. The second aim was to investigate age-related differences in dynamic and isometric measures of fatigue in response to cycling exercises. One of the novel aspects of her PhD research was the use of torque-velocity and power-velocity relationships obtained during cycling sprints to assess dynamic measures of fatigue. Due to the originality of her study, she was nominated as a finalist in the “Graduate Student Award Competition” organized by the Canadian Society for Exercise Physiology. Additionally, she received the “International Research Excellence Award”, which supported her to conduct her last PhD research project with Dr. Pierre Samozino in France.

Her main research interest is to develop exercise interventions targeted to improve muscle weakness and other physiological limitations that decrease the ability of older adults to perform activities of daily living. During her PhD, Renata focused on assessing the neuroprotective role of the exercise on counteracting the age-related changes in neuromuscular function. The neuromuscular function decline with aging leads to a greater incidence of falls and, consequently, to dependent living. Among the many consequences of attended living are poor sleep quality and cognitive impairment, which are the two pillars of her postdoctoral training.


Main results of the work we have done together

  • Neuromuscular fatigue induced by dynamic tasks is determined by exercise intensity and duration. While severe-intensity exercises induce more peripheral fatigue, fatigue after moderate-intensity exercise is associated with peripheral and central alterations.

  • Isometric force recovers from 10 s to 2 min after high-intensity exercise. Previous studies that have investigated neuromuscular fatigue with a delay of 2-3 min might have misinterpreted fatigue amplitude and etiology as well as the course of recovery.

  • Isometric and dynamic measures of fatigue are differently affected after a given exercise and the pattern of recovery for these measures is also different. We showed that maximal power output decreased more than maximal isometric force after the Wingate (-42 vs -19%) whereas maximal isometric force was more reduced than maximal power output after the 10-min (-38 vs -26%) and the 90-min (-27 vs -6%) tasks.

  • The assessment of fatigue (isometric force vs power) must be considered when identifying age-related neuromuscular fatigue mechanisms.

  • Age-related fatigue and recovery depend on the fatiguing exercise intensity and duration and on the fatigue assessment mode. Young males are as fatigable—for a Wingate and moderate-intensity exercises—or more fatigable—for severe-intensity exercise—than older participants. The inferred mechanism responsible for the greater fatigability response in young individuals is a greater metabolite accumulation.

  • Neuromuscular fatigue recovery in young males may be, at least partially, limited by factors related to prolongation of muscle relaxation time after a supramaximal exercise.

  • Cycling sprints load assignment should consider force production capacities rather than body mass. Sprints performed against an individualized calculated optimal load improve the fit of data in the torque-velocity and power-velocity curves.

  • Reducing the cycling sprint load for tests occurring at a fatigued state improves the fit of the data in the torque-velocity and power-velocity relationship curves.


Main publications associated with this work

Krüger RL, Peyrard A, di Domenico H, Rupp T, Millet GY, Samozino P. Optimal Load for a Force-Velocity Relationship Test During Cycling. European Journal of Applied Physiology (EJAP-D-20-00297). Status: minor revision.

Renata L Krüger, Saied Jalal Aboodarda, Libia Marcela Jaimes, Marco A Vaz, Pierre Samozino, Guillaume Y Millet. Age-Related Neuromuscular Fatigue and Recovery after Cycling: Measurements in Isometric and Dynamic Modes. Experimental Gerontology. 2020 May.

Renata L Krüger, Saied Jalal Aboodarda, Libia Marcela Jaimes, Pierre Samozino, Guillaume Y Millet . Cycling Exercises Performed at Different Intensities-Durations in Men: Neuromuscular Fatigue and Recovery Kinetics Revisited. Applied Physiology. Applied Physiology, Nutrition, and Metabolism. 2019 December.

Renata L Krüger, Saied Jalal Aboodarda, Libia Marcela Jaimes, Brian R MacIntosh, Pierre Samozino, Guillaume Y Millet.  Fatigue and Recovery Measured with Dynamic Properties vs Isometric Force: Effects of Exercise Intensity. The Journal of Experimental Biology. 2019 May 9

Renata L Krüger, Saied Jalal Aboodarda, Pierre Samozino, Charles L Rice, Guillaume Y Millet. Isometric versus Dynamic Measurements of Fatigue: Does Age Matter? A Meta-Analysis. Medicine and Science in Sports and Exercise. 2018 October.