Table 1.

Articles included in the review.

References	Type of Exercise	Type of Study	Study Sample	Results
Low-Intensity Exercise
Klein et al. (1994) [63]	4 h of treadmill exercise eliciting an oxygen uptake of 20 mL/kg/min.	Glycerol and free fatty acid rate of appearance and lipid oxidation were evaluated during basal resting conditions and after 4 h of treadmill exercise and 1 h of recovery.	n = 5 endurance-trained men; n = 5 untrained men.	After 4 h of exercise, the average glycerol and free fatty acid values, was similar in both trained and untrained subjects; but during recovery, glycerol and free fatty acid values decreased more rapidly in trained than in untrained subjects. Triglyceride oxidation was greater during exercise in the trained than in the untrained group.
Wolfe et al. (1990) [70]	4 h of treadmill exercise at 40% maximum O2 consumption, and 2 h of recovery.	Total fat oxidation was quantified by indirect calorimetry in response to exercise and in recovery from exercise.	n = 5 healthy male subjects.	Rate of appearance of glycerol and free fatty acids increased after 30 min and 4 h of exercise. Lipolysis decreased rapidly from the first 20 min to 2 h of recovery.
Verboven et al. (2018) [71]	12-week exercise training	Abdominal subcutaneous adipose tissue (SCAT) extracellular glycerol concentration and blood flow were measured using microdialysis at rest, during low-intensity endurance-type exercise and post-exercise recovery; at the same time, the response to α-/β-adrenoceptor was evaluated.	n = 10 healthy lean insulin-sensitive men n = 10 obese insulin-sensitive men n = 10 obese insulin-resistant men.	Exercise induce an increase of extracellular glycerol in SCAT in obese IS versus lean IS men: this could be the result of a lower blood flow in subcutaneous adipose tissue in obese IS men. Nonetheless, extracellular glycerol was blunted in obese IR versus obese IS men, despite comparable local blood flow after exercise. SCAT extracellular glycerol was reduced by 60% following local α-/β-adrenoceptor blockade in obese IS but not in obese IR men; in the latter, exercise training did not affect non- adrenergically-mediated lipolysis, despite an improved metabolic profile and body composition.
Moderate-Intensity Exercise
Chycki et al. (2019) [22]	Individuals belonging to the three groups were subjected to progressive exercise protocol on a treadmill at 30%, 50% and 70% VO2max, separated by 45 s of passive rest.	Venous blood was collected before, during and after exercise to determinate GH, noradrenaline, insulin, cortisol, glucose, FFA and glycerol.	n = 18 healthy trained and untrained men (32 ± 5.4 years): 6 obese subjects; 6 athletic subjects; 6 endurance-trained subjects.	Plasma glucose oxidation increased in relation to exercise intensity, especially in the athletic group, while plasma FFA level decreased with different kinetics in the three groups. Plasma GH increased immediately after exercise and remains high in all groups 45 min into recovery compared to rest. Plasma insulin decreased during exercise in all groups, but to a lesser extent in obese subjects.
O’Hearn et al. (2016) [52]	Two experimental trials conducted in the following way: 90 min baseline period in ambient temperature, followed by 120 min at rest and 30 min exercise at 50% VO2max at either 42 °C or 23 °C.	Metabolic data, heart rate, thermal responses and ventilation were measured throughout the baseline, passive periods and exercise period. Metabolic and ventilation measurements were recorded every 30 min. Blood samples were collected at baseline and 60 and 120 min of the passive period to determine changes in non-esterified fatty acid, TG, phospholipid and TC concentrations.	n = 8 healthy males (23–27 years).	Lipid oxidation rates were not different between heat (42 °C) and control (23 °C) conditions, as well as TG, phospholipid and TC levels. However, non-esterified fatty acid concentrations were significantly higher following passive heating (618 µM, 95% CI: 479–757) compared to control condition (391 µM, 95% CI: 270–511), and also following exercise (2036 µM, 95% CI: 1604–2469 for HEAT and 1351 µM, 95% CI: 1002–1699). * CI = confidence interval
	Four experimental trials that consist in a baseline period of 15-min (25 °C) and 60 min of exercise (walking at 50% VO2max in 0 °C; walking at 50% VO2max in 22 °C; running at 70% VO2max in 0 °C and running at 70% VO2max in 22 °C.	Thermal, cardiovascular and oxidative responses were measured every 15 min during exercise. Blood samples for serum non-esterified fatty acids, glycerol, glucose, beta-hydroxybutyrate, plasma catecholamines and serum lipids were collected immediately prior, and at 30 and 60 min of exercise.	n = 10 moderately active males (24.3 ± 3.0 years).	During submaximal walking and running, a rise in fat utilization in the cold was seen through lower respiratory quotient (RQ) (−0.03 ± 0.02), greater fat oxidation (+0.14 ± 0.13 g·min−1) and contribution of fat to total energy expenditure (+1.62 ± 1.99 kcal·min−1). However, serum non-esterified fatty acids, glycerol or catecholamine concentrations did not increase.
Petibois et al. (2002) [69]	A 10 Km run at the individual marathon velocity.	Blood triglycerides and glycerol and other biochemical parameters concentration, during exercise were analyzed.	n = 14 marathon runners (28–40 years)	Longer and/or less unsaturated blood fatty acids, a plasma triglyceride decrease, and a glycerol concentration increase were measured in the best runners
Nieman et al. (2017) [72]	Subjects ran on treadmills to exhaustion, with the speed set at 70% of VO2max.	Blood samples were collected before and after running to evaluate three cytokines, MCP-1, IL-6 and IL-8, and the stress hormones cortisol and epinephrine. Glycogen concentration was measured in vastus lateralis muscle biopsy. To study lipid metabolic profile was used three independent platforms: ultra-high performance liquid chromatography tandem mass spectrometry optimized for acidic or basic species and gas chromatography–mass spectrometry	n = 24 male runners (36.5 ± 1.8 years)	After running, muscle glycogen decreased (33.7% ± 4.2%), while MCP-1, IL-6 and IL-8 increased (1.4 ± 0.1-, 39.0 ± 8.8-, 2.4 ± 0.3-fold, respectively), such as cortisol and epinephrine (95.0% ± 18.9%, 158% ± 20.6%).The metabolomics analysis revealed changes in 209 metabolites, mostly long- and medium-chain fatty acids, fatty acid oxidation products (dicarboxylate and monohydroxy fatty acids, acylcarnitines) and ketone bodies. In this study, the relationship between IL-6 cytokine and adipose tissue lipolysis stimulation was not found.
Nieman et al. (2013) [73]	Subjects ran for 2.5 h/day on treadmills at ∼70% VO2max, for 3 days in a row.	75 metabolites, pre-exercise, immediately and 14 h post-exercise, were identified.	n = 15 long distance runners (7 males, 8 females; 19−45 years).	Of a total of 75 metabolites, increased immediately following the 3-day running period, 22 were related to lipid and carnitine metabolism, 13 to amino acid and peptide metabolism, 4 to hemoglobin and porphyrin metabolism and 3 to Krebs cycle intermediates (succinate, fumarate, and malate).
Laaksonen et al. (2018) [74]	Participants were divided into efficient (EF) and inefficient (IE) groups based on their mechanical efficiency at 45% of VO2 peak intensity during submaximal bicycle ergometer test.	During exercise, muscle blood flow, uptakes of oxygen, fatty acids and glucose were measured using positron emission tomography.	n = 17 healthy physically active male (EF: 24 ± 2 years; IE: 23 ± 2 years).	The use of blood glucose and intramuscular FA and glucose appeared to be similar between the two groups. However, EF group had increased muscle FA compared to IE group during exercise which led to higher usage of plasma FA, leading to think that use of plasma FA is important for mechanical efficiency during exercise.
Shaw et al. (2020) [75]	The endurance trained men had regularly competed in cycling and/or triathlon events within the last year, whereas the untrained group were physically active but did not complete regular endurance-type training.	Maximal fat oxidation and maximal oxygen uptake of the two groups was evaluated after exercise test on a cycle ergometer until exhaustion. Blood samples and biopsy were collected to assessed muscle fiber type and proteins involved in intramuscular lipids utilization by immunofluorescence microscopy and immunoblotting.	n = 7 endurance trained young males n = 8 untrained young males	Endurance-trained subjects displayed a higher maximal fat oxidation rate, a greater proportion of type I muscle fibers and higher intramuscular lipids content compared to untrained individuals. ATGL, HSL, PLIN 2, PLIN 5 and HAD content was ~2–3-fold higher in type muscle fibers compared to type IIa fibers. Consequently, these last were higher in endurance trained individuals.
Dandanell et al. (2018) [76]	A graded exercise test was performed	Plasma maximal rates of fat oxidation and VO2max were determined. Skeletal muscle biopsies were obtained to determine fatty acid oxidation and mitochondrial volume density.	n = 8 endurance-trained male cross-country skiers (20–22 years; VO2max 71 mL/min/kg); n = 8 healthy untrained male controls (23–24 years; VO2max 48 mL/min/kg).	VO2max, plasma maximal rate of fat oxidation, fatty acid oxidation and mitochondrial volume density were higher in the endurance-trained subjects compared to untrained subjects. The mitochondrial volume density, together with central adaptations as VO2max, determined the maximal rate of fat oxidation in endurance-trained subjects. Intrinsic mitochondrial changes were not associated with augmented maximal rate of fat oxidation.
Talanian et al. (2010) [77]	Six weeks of high-intensity interval training.	Biopsies were taken before and following 2 and 6 weeks of training from the vastus lateralis muscle.	n = 10 untrained females (22 ± 1 years)	High-intensity interval training increases fatty acid transport protein FAT/CD36 (10%) and FABPpm (48%) content in whole muscle; FABPpm and FAT/CD36 content increase in sarcolemmal (23%) and mitochondrial (51%) membranes in human skeletal muscle, respectively.
Jeppesen at al. (2012) [78]	Eight week aerobic training program at 45–80% VO2max, with increasing training frequency during the weeks.	FATP1 and FATP4 protein expression in the vastus lateralis muscle.	n = 8 healthy males (30 ± 1 years)	FATP4 protein content is increased (33%), whereas FATP1 protein content is reduced (20%) in skeletal muscle. FATP4 protein expression is related to lipid oxidation during endurance exercise.
Petridou et al. (2017) [79]	Participants cycled for 30 min at a heart rate of 130 to 140 beats per minute.	Subcutaneous adipose tissue was sampled at baseline and 5, 10, 20 and 30 min of exercise to determinate triacylglycerol lipase activity and expression; blood was collected for glycerol, non-esterified fatty acid, glucose, lactate, insulin, and catecholamine determination.	n = 16 healthy, sedentary men (20–26 years): lean group (n = 7; body mass index BMI ≤ 25 kg/m2; body fat < 15%) and an obese group (n = 9; BMI > 30 kg/m2; body fat > 20%).	Triacylglycerol lipase activity increased at 10 min of exercise in the lean men and returned to baseline at 20 and 30 min; in the obese men, it was higher than baseline at 10, 20 and 30 min and higher than the corresponding values in the lean men at 20 and 30 min. mRNA levels did not change during exercise, but the obese men had lower mRNA levels of ATGL, HSL and CGI-58 compared with the lean men.
High-Intensity Exercise
Romijin et al., (1993) [20]	Different exercise intensity was performed (25%, 65% or 85% of VO2max).	Plasma glucose tissue uptake and muscle glycogen oxidation were measured during the different exercise intensities.	n = 5 endurance-trained cyclists (24 ± 2 years; VO2max 67 ± 3 mL/min/kg)	Plasma glucose tissue uptake and muscle glycogen oxidation increased in relation to exercise intensity. During at higher intensities exercise, muscle triglyceride lipolysis was stimulated only whereas muscle glycogen and triglyceride oxidation decreased. During recovery from high-intensity exercise, the rate of lipolysis and release of fatty acids into plasma decreased.
Emed et al. (2016) [80]	The 24 h ultramarathon race was performed on an outdoor 400 m athletics track.	Total cholesterol, HDL, triglycerides, ApoB and ApoA1, before and after 400 m run, were assessed.	n = 14 male athletes (>18 years old).	No significant modifications in high-density lipoprotein, LDL and ApoA1 levels were measured. A reduction in ApoB levels correlated directly to the distance covered, and an increase in the LDL/ApoB ratio was observed. Lipid profile levels and oxidation of LDL were not acutely altered by prolonged physical activity.
Arakawa et al. (2016) [81]	2-day, 130 km ultramarathon.	Free fatty acids levels, after 1, 3 and 5/6 days 130 km ultramarathon were measured.	n = 18 runners (52.1 ± 12.1 years; BMI 21.1 ± 1.6 kg/m2).	Free fatty acids levels significantly enhanced during the race periods and stayed elevated after the race. Triglycerides declined on day 2 and day 3, and then returned to baseline level. HDL-C elevated on day 2 and remained elevated up to day 5. T-Chol concentrations decreased on day 2 and day 3, and afterward returned to baseline level.
Yanai et al. (2007) [82]	Participants were subjected to an incremental work test: 3 min of pedaling on a 15 W-loaded cycle ergometer increased by 15 W every minute.	Ventilatory threshold and serum FA changes were evaluated in all participants during exercise; blood samples were obtained at rest, peak work rate and 15 min after exercise.	n = 34 healthy female students (20.0 ± 1.0 years; BMI 20.6 ± 1.9): normal participants (n = 22) and participants with CD36 deficiency (n = 12).	Subjects with CD36 deficiency showed significantly lower ventilatory threshold than normal participants that was related to percentage changes in FA at peak work rate. In normal participants, serum FA levels decreased at peak work rate; in participants with CD36 deficiency, FA levels were not decreased at peak work rate and remained at significantly higher levels than normal participants 15 min after exercise.

* as a confidence interval.