Associations between Borg’s rating of perceived exertion and changes in urinary organic acid metabolites after outdoor weight-bearing hiking

Table 1 The Borg’s rating of perceived exertion scale (6-20)

Score	Perceived exertion
6	No exertion at all
7	Extremely light
8
9	Very light
10
11	Light
12
13	Somewhat hard
14
15	Hard
16
17	Very hard
18
19	Extremely hard
20	Maximal exertion

Table 2 Change of Borg’s rating of perceived exertion scale and organic acids

Compound	6-12 scale (n = 10), mean ± SD (range)	13-20 scale (n = 79), mean ± SD (range)	t	P value	Freedom	Effect size
Lactic acid	0.016 (0.013, 0.018), 0.008-0.038	0.028 ± 0.024 (0.010-0.150)	-2.933	0.006	32.954	-0.295
2-OH-isobutyric acid	0.003 ± 0.002 (0.001-0.006)	0.005 ± 0.003 (0.002-0.026)	-2.371	0.028	19.844	-0.279
Glycolic acid	0.246 ± 0.095 (0.098-0.393)	0.347 ± 0.115 (0.111-0.617)	-3.086	0.009	87	-0.431
2-OH-butyric acid	0.001 ± 0.000 (0.000-0.002)	0.002 ± 0.001 (0.001-0.008)	-5.425	0.000	26.692	-0.517
Glyoxylic acid	0.005 (0.004, 0.007), 0.004-0.010	0.009 (0.007, 0.011), 0.004-0.023	-4.554	0.000	14.629	-0.540
Oxalic acid	0.006 ± 0.003 (0.003-0.011)	0.008 ± 0.005 (0.000-0.031)	-1.382	0.182	20.192	-0.166
Pyruvic acid	0.026 ± 0.007 (0.013-0.036)	0.044 ± 0.021 (0.017-0.149)	-5.621	0.000	35.797	-0.503
3-OH-butyric acid	0.092 ± 0.035 (0.053-0.173)	0.219 ± 0.148 (0.054-1.025)	-2.689	0.009	87	-0.508
2-OH-isovaleric acid	0.007 ± 0.003 (0.004-0.013)	0.014 ± 0.009 (0.003-0.073)	-5.280	0.000	41.164	-0.468
2-methyl-3-OH-butyric acid	0.002 (0.002, 0.003), 0.001-0.015	0.004 (0.003, 0.006), 0.001-0.012	-3.159	0.002	87	-0.548
2-keto-isovaleric acid	0.001 ± 0.000 (0.000-0.001)	0.001 ± 0.001 (0.000-0.004)	-3.589	0.001	87	-0.614
Benzoic acid	0.001 (0.001, 0.001), 0.001-0.015	0.003 ± 0.002 (0.001-0.013)	-2.77	0.787	9.575	-0.056
2-keto-3-methylvaleric acid	0.001 ± 0.000 (0.000-0.001)	0.001 ± 0.001 (0.000-0.006)	-2.869	0.005	87	-0.535
Maleic acid	0.001 ± 0.000 (0.000-0.001)	0.001 ± 0.001 (0.000-0.003)	-4.047	0.001	16.432	-0.474
Succinic acid	0.007 ± 0.005 (0.002-0.019)	0.018 (0.013, 0.022), 0.005-0.032	-4.814	0.000	87	-0.673
Glyceric acid	0.003 ± 0.002 (0.001-0.006)	0.004 (0.003, 0.007), 0.002-0.014	-3.959	0.001	16.204	-0.468
Fumaric acid	0.019 ± 0.010 (0.004-0.042)	0.050 ± 0.030 (0.012-0.183)	-3.261	0.002	87	-0.573
Glutaric acid	0.002 ± 0.001 (0.000-0.004)	0.006 (0.004, 0.010), 0.002-0.018	-4.359	0.000	87	-0.684
3-methylglutaric acid	0.003 ± 0.003 (0.001-0.010)	0.006 (0.004, 0.009), 0.001-0.020	-3.262	0.006	13.322	-0.438
3-methylglutaconic acid	0.006 ± 0.004 (0.002-0.013)	0.016 ± 0.008 (0.004-0.043)	-6.149	0.000	19.746	-0.603
Glutaconic acid	0.006 ± 0.004 (0.001-0.014)	0.016 ± 0.011 (0.001-0.052)	-2.857	0.005	87	-0.516
Decanoic acid	0.000 (0.000, 0.001), 0.000-0.001	0.001 (0.001, 0.001), 0.000-0.004	-2.754	0.007	87	-0.486
Malic acid	0.002 (0.002, 0.004), 0.001-0.010	0.009 ± 0.008 (0.001-0.057)	-4.364	0.000	29.065	-0.429
Adipic acid	0.006 ± 0.007 (0.001-0.024)	0.019 ± 0.021 (0.003-0.123)	-3.932	0.000	35.442	-0.378
Creatinine	2.717 ± 3.056 (0.279-10.426)	5.955 ± 3.663 (0.012-13.452)	-3.157	0.008	12.488	-0.433
Mandelic acid	0.002 ± 0.002 (0.001-0.003)	0.003 ± 0.001 (0.001-0.007)	-5.460	0.000	15.516	-0.598
2-OH-glutaric acid	0.006 ± 0.003 (0.002-0.013)	0.017 ± 0.009 (0.000-0.044)	-3.867	0.000	87	-0.634
Pimelic acid	0.002 ± 0.001 (0.000-0.004)	0.005 ± 0.003 (0.000-0.014)	-3.978	0.000	87	-0.645
2-keto-glutaric acid	0.002 ± 0.003 (0.000-0.009)	0.020 ± 0.013 (0.000-0.087)	-4.268	0.000	87	-0.684
Phenylpyruvic acid	0.013 ± 0.008 (0.005-0.032)	0.034 (0.023, 0.043), 0.005-0.136	-7.031	0.000	31.925	-0.599
Aconitic acid	0.002 (0.001, 0.012), 0.000-0.028	0.053 ± 0.041 (0.001-0.174)	-8.287	0.000	64.322	-0.605
Vanillic acid	0.023 ± 0.025 (0.001-0.075)	0.035 (0.016, 0.080), 0.000-0.357	-3.146	0.004	27.007	-0.330
Homovanillic acid	0.011 (0.007, 0.017), 0.004-0.060	0.044 ± 0.022 (0.009-0.129)	-4.900	0.000	13.464	-0.588
Azelaic acid	0.008 ± 0.007 (0.000-0.022)	0.017 ± 0.012 (0.002-0.084)	-3.418	0.003	16.749	-0.410
Citric acid	0.001 ± 0.001 (0.000-0.003)	0.005 ± 0.005 (0.000-0.030)	-2.517	0.014	87	-0.487
Sebacic acid	0.078 (0.042, 0.168), 0.023-0.481	0.252 ± 0.183 (0.034-1.039)	-2.135	0.053	12.500	-0.316
Palmitic acid	0.025 ± 0.007 (0.014-0.033)	0.040 ± 0.012 (0.024-0.095)	-6.076	0.000	16.511	-0.627

Table 3 Differential organic acid metabolites between Borg’s rating of perceived exertion 6-12 scale and 13-20 scale

Compound	KEGG ID	VIP	Fold change	P value
Succinic acid	C00042	1.38	2.45	0.000
Homovanillic acid	C05582	1.29	2.76	0.000
Glutaric acid	C00489	1.27	3.52	0.000
Palmitic acid	C00249	1.25	1.64	0.000
3-methylglutaconic acid	-	1.21	2.64	0.000
Pimelic acid	C02656	1.19	3.54	0.000
2-keto-glutaric acid	C00026	1.19	8.52	0.000
2-OH-glutaric acid	-	1.18	3.00	0.000
Mandelic acid	C01984	1.16	1.91	0.000
Glyoxylic acid	C00048	1.15	1.63	0.000
3-methylglutaric acid	-	1.11	2.08	0.006
2-keto-isovaleric acid	-	1.09	2.01	0.001
Aconitic acid	C00417	1.08	7.11	0.000
Phenylpyruvic acid	C00166	1.08	2.92	0.000
Glutaconic acid	C02214	1.05	2.64	0.005
2-methyl-3-OH-butyric acid	-	1.04	2.00	0.002
2-OH-butyric acid	C05984	1.04	1.89	0.000
Fumaric acid	C00122	1.01	2.66	0.002
Creatinine	C00791	1.00	2.22	0.008

KEGG: Kyoto encyclopedia of genes and genomes; VIP: Variable importance in the projection.