https://doi.org/10.5061/dryad.08kprr59v

Description of the data and file structure

2024_808F_Ergometer_Design_Dryad.pdf

Figure 1 shows the ergometer built from non-magnetic material (wood, plastic, aluminum). The ergometer fits into a commonly available 3T Siemens scanner where MRI/MRS methods can then follow the metabolism in exercising muscle.

Figure 2 shows the position of the subject’s leg in the ergometer. The slider, a sliding component, rests on the subject’s ankle. As the subject’s leg kicks, the foot pushes against the slider and raises it toward a stop plate. The slider’s travel distance from rest to the stop plate defines a critical parameter in calculating work. A weight placed on the foot sets the workload.

Figure 3 shows the ergometer positioned in a 3-T scanner. A surface coil resting on top of the leg detects the MRS signal during and after exercise. Slots in the ergometer allow straps to anchor the unit to the scanner bed.

Figure 4 shows the time resolved 31P NMR spectra from human quadriceps before, during, and after exercise. Each spectrum corresponds to an averaged signal acquired every 6s as the subject kicks at 1Hz against a load approximating 10% of maximal voluntary contraction (MVC). 

Figure 5 Select spectra before, during, and after exercise show the signals of PCr at -2.54 ppm; inorganic phosphate (Pi) at 2.30 ppm; and γ-ATP, ⍺-ATP, and β-ATP at -4.81 ppm, -10.00 ppm, -18.50 ppm, respectively. 

Figure 6 shows the modeling of the PCr recovery kinetics after exercise using the exponential equation:

 PCr(t)= PCr(0) + ΔPCr(1-e-kt)

where t = time; k = rate constant; PCr(0) = [PCr] at the beginning of exercise recovery;  ΔPCr = PCr(rest)-PCr(0) [1,2]. Studies have established that the rate constant of PCr recovery kinetics can assess the muscle mitochondrial bioenergetics in broad range of subjects, including those with chronic kidney disease [3].  

Solid black circles represent collected data. Time zero on the x-axis corresponds to the beginning of exercise recovery. PCr drops 20% from its resting level at the start of recovery. The exponential rate constant for PCr recovery is 3.15 min-1. Upper and lower bounds indicate 95% confidence intervals.

Figure 7 displays the pH profile as reflected in the chemical shift of the Pi peak, as calculated from the equation:

where δo = observed chemical shift of the Pi signal; δA = ppm of [H2PO41-] at 3.290 ppm, δB = ppm\
of [HPO42-] at 5.805 ppm. The PCr signal at -2.54 ppm serves as the chemical shift reference.

After the control period, the exercise begins and continues for 42s. A recovery phase follows for the next 360s. The control pH of 7.03 shifts slightly to 7.05 during exercise and returns to 7.02 after exercise, table 1.

Excel spreadsheet contains the raw 31P MRS data of phosphocreatine (PCr) and inorganic phosphate (Pi) collected from 3 independent experiments on a subject during the control period, exercise, and post-exercise recovery. The data show the PCr chemical shift, PCr signal intensity, the Pi chemical shift relative to PCr, and the Pi signal amplitude. 

Files and variables

File: 2024_808F_Ergometer_Design_Dryad.pdf

Description: File contains ergometer specifications, its setup in exercising subject's leg in the magnet, the resultant 31P NMR signals detected during exercise and post-exercise, the nonlinear fit of the phosphocreatine (PCr) recovery data, the pH profile during exercise and post-exercise, and a table with pH and PCr values at different time points in the experiment.

File: 2024_829_Ergometer_Dryad_Raw__V3.xlsx

Description: File contains the raw 31P MRS data collected from the quadriceps of a subject during rest, exercise, and post-exercise recovery.  The numbers 1, 2, and 3 correspond to the 3 distinct experiments.

Spectra:  Spectrum number identifies the spectrum collected.  Each spectrum corresponds to the signal averaging of 6 blocks of data.  Each data block requires 1s of signal acquisition. Total signal averaging time for each spectrum = 6s. The signal acquisition starts at t=0 and completes in 6s to create the 1st spectrum.  After the collecting the 1st spectrum, the spectrometer commences immediately to acquire the next spectrum. The process continues, until the signal acquisition stops after the collection of the 75th spectrum.

Time, min:  Conversion of time unit from seconds to minutes.

PCr, δppm:  Chemical shift of the PCr peak in parts per million (ppm)

PCr, signal amplitude:  Signal intensity of the PCr signal.

Pi, δppm:  Chemical shift of the Pi peak in parts per million (ppm)

Pi, signal amplitude:  Signal intensity of the Pi signal.

References

[1]        R.A. Meyer, A linear model of muscle respiration explains monoexponential phosphocreatine changes, American Journal of Physiology 254 (1988) C548-C553.

[2]        M. Meyerspeer, C. Boesch, D. Cameron, M. Dezortova, S.C. Forbes, A. Heerschap, J.A.L. Jeneson, H.E. Kan, J. Kent, G. Layec, J.J. Prompers, H. Reyngoudt, A. Sleigh, L. Valkovic, G.J. Kemp, Experts' Working Group on, 31P magnetic resonance spectroscopy in skeletal muscle: Experts' consensus recommendations, NMR Biomed 34(5) (2020) e4246. https://doi.org/10.1002/nbm.4246.

[3]        B. Kestenbaum, J. Gamboa, S. Liu, A.S. Ali, E. Shankland, T. Jue, C. Giulivi, L.R. Smith, J. Himmelfarb, I.H. de Boer, K. Conley, B. Roshanravan, Impaired skeletal muscle mitochondrial bioenergetics and physical performance in chronic kidney disease, JCI Insight 5(5) (2020). https://doi.org/10.1172/jci.insight.133289.

[4]        J.B. de Araujo Ribeiro Alvares, R. Rodrigues, R. de Azevedo Franke, B.G. da Silva, R.S. Pinto, M.A. Vaz, B.M. Baroni, Inter-machine reliability of the Biodex and Cybex isokinetic dynamometers for knee flexor/extensor isometric, concentric and eccentric tests, Phys Ther Sport 16(1) (2015) 59-65. https://doi.org/10.1016/j.ptsp.2014.04.004.

[5]        D.C. Feiring, T.S. Ellenbecker, G.L. Derscheid, Test-retest reliability of the biodex isokinetic dynamometer, J Orthop Sports Phys Ther 11(7) (1990) 298-300. https://doi.org/10.2519/jospt.1990.11.7.298.