Do Putative Human Reticulospinal Tract Properties Adapt Following Short-Term Isometric Resistance Training?

PURPOSE: The primary purpose of this study was to investigate whether isometric resistance training (RT) leads to reticulospinal tract (RST) adaptations. METHODS: A "RT group" of 30 healthy adults completed 4 weeks (15 sessions) of volume-matched unilateral elbow flexion RT involving high (32 repetitions/session at 70% maximal voluntary torque [MVT]) or low (64 repetitions/session at 35%MVT) loads. An additional 15 participants served as controls (CON group). Pre- and post-test MVT, RST properties (RST gain ratio derived from the StartReact assessment; startling auditory stimulus-conditioned/control motor evoked potential [MEP] ratio; and startling stimulus-conditioned/control cervicomedullary MEP [CMEP] ratio), CST excitability and intracortical inhibition properties (in response to transcranial magnetic stimulation) were assessed. RESULTS: MVT increased more in the RT group (+12.8%; n = 30) vs. CON group (-4.3%; n = 15; group (2) × time (2), p = 0.001). However, changes in RST properties assessed using a series of indirect measures did not differ between the RT group (-1.4% to 6.6%; n = 30) and CON group (-4.5% to 10.5%; n = 15; group (2) × time (2), 0.352 ≤ p ≤ 0.834). CONCLUSIONS: RST adaptations within a sample of healthy young men and women, assessed using various indirect measurement approaches, did not occur following only 4 weeks of isometric elbow flexion RT. These findings add to the currently limited scientific evidence from short-term human RT intervention studies available to inform the use of RT for healthy individuals or patients primarily targeting the development of RST function.