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Maximal Fat Oxidation & FatMax Function

Source: R/MFO.R
MFO.Rd

Calculate Maximal Fat Oxidation (MFO), the exercise intensity that elicits MFO (FatMax), the FatMax zone, and the crossover point. Supports multiple methods to locate MFO (P3, P2, MV, MRER) and stoichiometric equations (Frayn, Jeukendrup, Peronnet).

Usage

MFO(
  step_time,
  db_MFO,
  db_basal,
  db_graded = NULL,
  cv_var,
  author,
  VO2max = NULL,
  method = "P3",
  step_duration = 180,
  steady_state_duration = 60,
  RER_cutoff = NULL,
  negative_FAT = "truncate",
  body_mass = NULL,
  fat_free_mass = NULL,
  HRmax = NULL,
  vo2max_window = 30,
  include_basal = FALSE,
  energy_equivalents = c("classic", "source"),
  use_incomplete_step = FALSE,
  min_steps = 6
)

Arguments

step_time

how often the data was collected (in seconds).

db_MFO

database containing MFO test.

db_basal

database containing basal test.

db_graded

database containing incremental exercise test (optional if VO2max provided). VO2max is the highest mean VO2 over `vo2max_window` seconds of consecutive records.

cv_var

variable to estimate coefficient of variation. Can be: "VO2", "VCO2" or "RER".

author

author to estimate MFO. Can be: "Frayn", "Jeukendrup" or "Peronnet". "Jeukendrup" warns when an exercise step is outside 40-75 % VO2max, the range of Jeukendrup & Wallis (2005, Table 5); the resting row never warns.

VO2max

VO2max can be passed directly (ml/min) instead of using db_graded. If both are given, `VO2max` is used as is and `db_graded` is ignored with a warning.

method

method to locate MFO and Fatmax: "P3" (3rd-degree polynomial, default), "P2" (2nd-degree polynomial), "MV" (measured values) or "MRER" (RER method). See the section *Methods*.

step_duration

duration of each exercise step in seconds (default 180 = 3 min).

steady_state_duration

duration of steady-state period to average within each step, in seconds (default 60).

RER_cutoff

RER value above which steps are excluded (default NULL = no cutoff), as a number or by name, following Amaro-Gahete et al. (2019, Front Physiol 10: 909, doi:10.3389/fphys.2019.00909 ): "classic" = 1.00 (Cheneviere et al. 2009 averaged only steps with RER <= 1.0); "safe" = 0.95, the end-of-test RER they recommend as safe to capture MFO; "sedentary" = 0.93 and "trained" = 0.90, the mean RER at MFO they report in those groups. Low cutoffs leave few steps (SPEC 4, 19 finding 2).

negative_FAT

how to handle negative fat oxidation values: "truncate" (set to 0, default), "exclude" (remove from fitting), or "keep" (include in fitting).

body_mass

body mass in kg (optional, for relative MFO calculation).

fat_free_mass

fat-free mass in kg (optional, for FFM-relative MFO calculation).

HRmax

maximum heart rate in bpm (optional, for FatMax as %HRmax).

vo2max_window

averaging window in seconds for VO2max from `db_graded` (default 30). If it is not a multiple of `step_time`, the number of records is rounded up (30 s with 20-s records uses 2 records = 40 s). See SPEC 9.5 and 14.

include_basal

logical. If `TRUE`, the resting row (from `db_basal`) enters `MFO_db` as step 0 and is part of the curve fit, as in Montes de Oca et al. (2021, Eur J Sport Sci, doi:10.1080/17461391.2020.1788650 ). Default `FALSE` fits exercise steps only and reproduces v0.1.0/v0.2.0, which dropped the resting row. With `TRUE` the P3/P2 fit changes; the resting row has `HR = NA` and `Load = "basal"`. See SPEC 9.5.

energy_equivalents

kcal per g used for `Kcal` and `x_Kcal`: "classic" (4 kcal/g CHO, 9 kcal/g FAT, as in v0.2.0) or "source" (values of the source of `author`: Peronnet & Massicotte 1991 for "Peronnet" and, as a package decision, "Frayn"; Jeukendrup & Wallis 2005, Table 5, for "Jeukendrup"). Default "classic" in 0.2.x; it will change to "source" in 0.3.0, and a message says so once per session when the argument is not set. MFO and Fatmax (g/min) do not depend on it. See [substrate_oxidation()] and SPEC 19 (finding 1).

use_incomplete_step

logical. Records left after the last complete step (fewer than `step_duration` s) always give a warning stating "X s of Y s". With `FALSE` (default, as in v0.2.0) they are dropped. With `TRUE` that incomplete step is used only if it lasts at least `steady_state_duration`; its last `steady_state_duration` s are averaged, as for complete steps, although VO2 may not have reached its plateau. See SPEC 9.5.

min_steps

minimum number of exercise steps recommended for the fit (default 6). A warning is given when fewer steps remain after `RER_cutoff` and `negative_FAT = "exclude"`; the resting row of `include_basal = TRUE` does not count. See SPEC 14.

Value

Returns a list which contains:

  • MFO_db: database with Load, VO2, VCO2, HR, RER, CHO, FAT, Kcal, porc_VO2 (one row per exercise step, plus the resting row first if `include_basal = TRUE`).

  • MFO_plot: ggplot object with the MFO plot including FAT and CHO curves.

  • MFO: Maximal fat oxidation (g/min).

  • MFO_relative: MFO relative to body mass (mg/kg/min), if body_mass provided.

  • MFO_FFM: MFO relative to fat-free mass (mg/kgFFM/min), if fat_free_mass provided.

  • FAT_MAX: Intensity that elicits MFO (% VO2max).

  • FAT_MAX_HR: Heart rate at FatMax (bpm), interpolated from data.

  • FAT_MAX_porcHRmax: FatMax as % HRmax, if HRmax provided.

  • FatMax_zone_lower: Lower bound of FatMax zone (% VO2max).

  • FatMax_zone_upper: Upper bound of FatMax zone (% VO2max).

  • FatMax_zone_method: "fitted curve", or "linear interpolation" for `method = "MV"`.

  • crossover_point: Intensity at which CHO > FAT (% VO2max).

  • R_squared: R-squared of the fitted model (`NA` for "MV").

  • RMSE: Root mean squared error of the fitted model (`NA` for "MV").

  • method: Method used for curve fitting.

  • energy_equivalents: energy equivalents used for `Kcal` ("classic" or "source").

  • VO2max: VO2max used to express intensity (ml/min).

  • VO2max_window: effective averaging window for VO2max (s); NA if VO2max was supplied.

  • VO2max_window_requested: `vo2max_window` as requested (s); NA if VO2max was supplied.

  • x_CHO: carbohydrates in basal metabolism (g/min), with the same `author` equations as the test.

  • x_FAT: fat in basal metabolism (g/min).

  • x_Kcal: Kcal in basal metabolism (kcal/min).

Quality warnings

Besides the warnings on inputs, `MFO()` warns when the result needs checking (SPEC 9.5, 14):

  • fewer than `min_steps` exercise steps enter the fit;

  • Fatmax is at the edge: the exercise step nearest to Fatmax is the first or the last one (resting row excluded), so the maximum may lie outside the measured range (the test started too high or stopped too early);

  • the last step is incomplete (see `use_incomplete_step`);

  • HR is missing: `FAT_MAX_HR` and `FAT_MAX_porcHRmax` are `NA`, or interpolated from fewer steps. HR never removes steps from the fit.

Methods

  • `"P3"`, `"P2"`: least-squares polynomial of FAT on % VO2max; Fatmax is the maximum of the fitted curve within the measured range (SPEC 6.2, 6.3).

  • `"MV"` (measured values): Fatmax is the step with the highest observed FAT, computed with the `author` equations; MFO is that FAT. No model is fitted, so `R_squared` and `RMSE` are `NA`; the curve drawn and the Fatmax zone use linear interpolation between steps (`FatMax_zone_method = "linear interpolation"`). SPEC 6.1.

  • `"MRER"`: procedure of Cheneviere et al. (2009, p. 1617, doi:10.1249/MSS.0b013e31819e2f91 ), after Perez-Martin et al. (2001). (1 - RER) and VO2 are fitted as straight lines of % VO2max, 1 - RER = a1 + b1 x and VO2 = a2 + b2 x, so fat oxidation 1.7 (1 - RER) VO2 is a parabola whose vertex, x = -(a1 b2 + a2 b1) / (2 b1 b2), gives Fatmax, and its value MFO (g/min). This uses the 1.7 (1 - RER) VO2 simplification of Peronnet & Massicotte whatever `author` is. If the parabola has no maximum or the vertex lies outside the measured range, `"MV"` is used with a warning. SPEC 3, 6.1.

Up to v0.2.0, `"MRER"` returned the step with the highest observed 1.7 (1 - RER) VO2, which is a measured-values method: use `"MV"` for that behaviour (same step; MFO from the `author` equation). SPEC 19, finding 4.

Examples


if (FALSE) { # \dontrun{
# Read dfs
data(list = c("basal_df", "MFO_df", "VO2max_df"), package = "MFO")

# Convert to data.frame
basal_df <- data.frame(basal_df)
MFO_df <- data.frame(MFO_df)
VO2max_df <- data.frame(VO2max_df)

# Calculate MFO and Fatmax (P3 method)
result_MFO <- MFO(step_time = 20,
                 db_MFO = MFO_df,
                 db_basal = basal_df,
                 db_graded = VO2max_df,
                 cv_var = "RER",
                 author = "Frayn",
                 method = "P3")

# With all options
result_MFO <- MFO(step_time = 20,
                 db_MFO = MFO_df,
                 db_basal = basal_df,
                 db_graded = VO2max_df,
                 cv_var = "RER",
                 author = "Frayn",
                 method = "P3",
                 RER_cutoff = 1.0,
                 body_mass = 75,
                 fat_free_mass = 60,
                 HRmax = 190)
} # }