Vitamin B12 deficiency can cause digestive problems like diarrhea, constipation, or loss of appetite
For weekend warriors and recreational athletes alike, B12 injections may help bridge the gap between nutritional needs and actual intake, especially when training demands increase
Not trying to frighten you but if this is the cause (and I'm not saying it is), the consequences can be so severe that it's really important to consult a medical practitioner, as a matter of urgency, to either rule it out or access immediate treatment

ACTH adrenocorticotropic hormone AD Alzheimer's disease ALLO allopregnanolone AMPA -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ANT adenine nucleotide transporter protein BBB blood-brain barrier BNST bed nucleus of the stria terminalis CB1 cannabinoid receptor 1 CICR Ca 2+ -induced Ca 2+ release CNS central nervous system DA dopamine DAT dopamine transporter DAT KO dopamine transporter knockout DHEA dehydroepiandrosterone DHEAS dehydroepiandrosterone sulfate GABA gamma-aminobutyric acid GAD generalized anxiety disorder GLIC Gloeobacter ligand-gated ion channels GnRH gonadotrophin-releasing hormone HPA axis hypothalamic-pituitary-adrenal axis HRSA Hamilton Rating Scale for Anxiety IL-6 interleukin-6 L-Type VGCC L-type voltage-gated Ca 2+ channel LTD long-term depression LTP long-term potentiation MCI mild cognitive impairment NMDA N-methyl-D-aspartate OATPs organic anion transporting peptides ORAI1 Ca 2+ release-activated Ca 2+ channel protein 1 PAHS pregnanolone hemisuccinate pCREB phosphorylated CREB PET positron emission tomography PCOS polycystic ovary syndrome PREG pregnenolone PregS pregnenolone sulfate PTSD post-traumatic stress disorder PV parvalbumin PXR pregnane xenobiotic receptor P450 scc cytochrome P450 side chain cleavage sEPSC spontaneous excitatory post-synaptic currents 5-HT serotonin SSRIs selective serotonin reuptake inhibitors StAR protein steroidogenic acute regulatory protein STIM1 stromal interaction molecule 1 THDOC tetrahydrodeoxycorticosterone TRH thyrotropin-releasing hormone TRP channels transient receptor potential channels TSPO translocator protein VDAC voltage-dependent anion channel

Over a full year, more consistent training can absolutely translate into better strength and physique outcomes, but the muscle gain comes from the training, not the peptide