@article{SperlichHahnEdeletal.2018,
  author    = {Sperlich, Billy and Hahn, Lea-Sofie and Edel, Antonia and Behr, Tino and Helmprobst, Julian and Leppich, Robert and Wallmann-Sperlich, Birgit and Holmberg, Hans-Christer},
  title     = {A 4-week intervention involving mobile-based daily 6-minute micro-sessions of functional high-intensity circuit training improves strength and quality of life, but not cardio-respiratory fitness of young untrained adults},
  series = {Frontiers in Physiology},
  volume    = {9},
  journal   = {Frontiers in Physiology},
  number    = {423},
  doi       = {10.3389/fphys.2018.00423},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-176565},
  year      = {2018},
  abstract  = {The present study was designed to assess the psycho-physiological responses of physically untrained individuals to mobile-based multi-stimulating, circuit-like, multiple-joint conditioning (Circuit\(_{HIIT}\)) performed either once (1xCircuitHIIT) or twice (2xCircuit\(_{HIIT}\)) daily for 4 weeks. In this single-center, two-arm randomized, controlled study, 24 men and women (age: 25 ± 5 years) first received no training instructions for 4 weeks and then performed 4 weeks of either 1xCircuitHIIT or 2xCircuit\(_{HIIT}\) (5 men and 7 women in each group) daily. The 1xCircuitHIIT and 2xCircuit\(_{HIIT}\) participants carried out 90.7 and 85.7\% of all planned training sessions, respectively, with average heart rates during the 6-min sessions of 74.3 and 70.8\% of maximal heart rate. Body, fat and fat-free mass, and metabolic rate at rest did not differ between the groups or between time-points of measurement. Heart rate while running at 6 km⋅h\(^{-1}\) declined after the intervention in both groups. Submaximal and peak oxygen uptake, the respiratory exchange ratio and heart rate recovery were not altered by either intervention. The maximal numbers of push-ups, leg-levers, burpees, 45°-one-legged squats and 30-s skipping, as well as perception of general health improved in both groups. Our 1xCircuit\(_{HIIT}\) or 2xCircuit\(_{HIIT}\) interventions improved certain parameters of functional strength and certain dimensions of quality of life in young untrained individuals. However, they were not sufficient to enhance cardio-respiratory fitness, in particular peak oxygen uptake.},
  language  = {en}
}
@article{DuekingGiessingFrenkeletal.2020,
  author    = {D{\"u}king, Peter and Giessing, Laura and Frenkel, Marie Ottilie and Koehler, Karsten and Holmberg, Hans-Christer and Sperlich, Billy},
  title     = {Wrist-Worn Wearables for Monitoring Heart Rate and Energy Expenditure While Sitting or Performing Light-to-Vigorous Physical Activity: Validation Study},
  series = {JMIR mhealth and uhealth},
  volume    = {8},
  journal   = {JMIR mhealth and uhealth},
  number    = {5},
  doi       = {10.2196/16716},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229413},
  year      = {2020},
  abstract  = {Background: Physical activity reduces the incidences of noncommunicable diseases, obesity, and mortality, but an inactive lifestyle is becoming increasingly common. Innovative approaches to monitor and promote physical activity are warranted. While individual monitoring of physical activity aids in the design of effective interventions to enhance physical activity, a basic prerequisite is that the monitoring devices exhibit high validity. Objective: Our goal was to assess the validity of monitoring heart rate (HR) and energy expenditure (EE) while sitting or performing light-to-vigorous physical activity with 4 popular wrist-worn wearables (Apple Watch Series 4, Polar Vantage V, Garmin Fenix 5, and Fitbit Versa). Methods: While wearing the 4 different wearables, 25 individuals performed 5 minutes each of sitting, walking, and running at different velocities (ie, 1.1 m/s, 1.9 m/s, 2.7 m/s, 3.6 m/s, and 4.1 m/s), as well as intermittent sprints. HR and EE were compared to common criterion measures: Polar-H7 chest belt for HR and indirect calorimetry for EE. Results: While monitoring HR at different exercise intensities, the standardized typical errors of the estimates were 0.09-0.62, 0.13-0.88, 0.62-1.24, and 0.47-1.94 for the Apple Watch Series 4, Polar Vantage V, Garmin Fenix 5, and Fitbit Versa, respectively. Depending on exercise intensity, the corresponding coefficients of variation were 0.9\%-4.3\%, 2.2\%-6.7\%, 2.9\%-9.2\%, and 4.1\%-19.1\%, respectively, for the 4 wearables. While monitoring EE at different exercise intensities, the standardized typical errors of the estimates were 0.34-1.84, 0.32-1.33, 0.46-4.86, and 0.41-1.65 for the Apple Watch Series 4, Polar Vantage V, Garmin Fenix 5, and Fitbit Versa, respectively. Depending on exercise intensity, the corresponding coefficients of variation were 13.5\%-27.1\%, 16.3\%-28.0\%, 15.9\%-34.5\%, and 8.0\%-32.3\%, respectively. Conclusions: The Apple Watch Series 4 provides the highest validity (ie, smallest error rates) when measuring HR while sitting or performing light-to-vigorous physical activity, followed by the Polar Vantage V, Garmin Fenix 5, and Fitbit Versa, in that order. The Apple Watch Series 4 and Polar Vantage V are suitable for valid HR measurements at the intensities tested, but HR data provided by the Garmin Fenix 5 and Fitbit Versa should be interpreted with caution due to higher error rates at certain intensities. None of the 4 wrist-worn wearables should be employed to monitor EE at the intensities and durations tested."},
  language  = {en}
}
@article{DuekingZinnerReedetal.2020,
  author    = {D{\"u}king, Peter and Zinner, Christoph and Reed, Jennifer L. and Holmberg, Hans-Christer and Sperlich, Billy},
  title     = {Predefined vs data-guided training prescription based on autonomic nervous system variation: A systematic review},
  series = {Scandinavian Journal of Medicine \& Science in Sports},
  volume    = {30},
  journal   = {Scandinavian Journal of Medicine \& Science in Sports},
  number    = {12},
  doi       = {10.1111/sms.13802},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217893},
  pages     = {2291 -- 2304},
  year      = {2020},
  abstract  = {Monitoring variations in the functioning of the autonomic nervous system may help personalize training of runners and provide more pronounced physiological adaptations and performance improvements. We systematically reviewed the scientific literature comparing physiological adaptations and/or improvements in performance following training based on responses of the autonomic nervous system (ie, changes in heart rate variability) and predefined training. PubMed, SPORTDiscus, and Web of Science were searched systematically in July 2019. Keywords related to endurance, running, autonomic nervous system, and training. Studies were included if they (a) involved interventions consisting predominantly of running training; (b) lasted at least 3 weeks; (c) reported pre- and post-intervention assessment of running performance and/or physiological parameters; (d) included an experimental group performing training adjusted continuously on the basis of alterations in HRV and a control group; and (e) involved healthy runners. Five studies involving six interventions and 166 participants fulfilled our inclusion criteria. Four HRV-based interventions reduced the amount of moderate- and/or high-intensity training significantly. In five interventions, improvements in performance parameters (3000 m, 5000 m, Loadmax, Tlim) were more pronounced following HRV-based training. Peak oxygen uptake (VO\(_{2peak}\)) and submaximal running parameters (eg, LT1, LT2) improved following both HRV-based and predefined training, with no clear difference in the extent of improvement in VO\(_{2peak}\). Submaximal running parameters tended to improve more following HRV-based training. Research findings to date have been limited and inconsistent. Both HRV-based and predefined training improve running performance and certain submaximal physiological adaptations, with effects of the former training tending to be greater.},
  language  = {en}
}