*CNTF* and *CNTFR*

Two studies examined the Ciliary Neurotrophic Factor (*CNTF*) and Ciliary Neurotrophic Factor Receptor (*CNTFR*) genes (Table 2). In 2006, Arking et al. [25] observed five DNA polymorphisms (rs948562, rs1800169, rs550942, rs4319530, rs1938596) of the *CNTF* gene to be significantly associated with HG strength (*p* < 0.05). Further haplotype analysis revealed the null allele (A) of rs1800169 to fully explain this relationship under a recessive model. Individuals homozygous for the A allele had 3.8 kg lower HG strength than G allele carriers (*p* < 0.01). Interestingly, De Mars et al. [36] found only G/A carriers of the rs1800169 polymorphism to have significantly lower KE strength than G/G or A/A carriers (*p* = 0.0229). Additionally, male T allele carriers of the rs3808871 polymorphism produced significantly higher KE and knee flexor (KF) isometric torque at 120◦ when compared to CC homozygotes (*p* < 0.05). Furthermore, females who carried the T allele of the rs2070802 polymorphism produced greater KF concentric torques than the A/A homozygotes (*p* = 0.04).

### *TNF*α

Three studies were included in this review which investigated the Tumour Necrosis Factor Alpha (*TNF*α) gene, each with significant findings. In 2013, Pereira et al. [65] observed that G allele homozygotes of the rs1800629 polymorphism achieved significantly faster timed up and go (TUG) test results in response to 10 weeks of RT compared to A allele carriers (*p* < 0.001). Additionally, Tiainen et al. [69] found the A allele of the rs361525 polymorphism to be associated with a significantly better physical performance level compared to GG homozygotes (*p* < 0.001). Finally, Li et al. [53] highlighted the interaction between the A allele of the rs1799964 polymorphism with either the G allele of the Tumour Necrosis Factor Beta (*TNF-*β) rs909253 polymorphism or the A allele of the *TNF-*β rs1041981 polymorphism to result in significantly lower handgrip strength among females (*p* = 0.005, *p* = 0.006 respectively).

### Other Genes

Polymorphisms rs2276541 of the activin A type IIB receptor (*ACVR2B*) gene, rs3807987 of Caveolin 1 (*CAV1*) gene and rs1805086 of the Myostatin (*MSTN*) gene were all significantly associated with FFM (Table 2) [41,49,56].

#### 3.5.3. Structural and Metabolic Genes
