Proceedings of The Physiological Society

Physiology 2016 (Dublin, Ireland) (2016) Proc Physiol Soc 37, PCB165

Poster Communications

Peripheral muscle fatigue is linked to type-II cross sectional area in the elderly

J. M. Kröpfl1, J. Bondietti2, T. U. Wüthrich3, D. Aguayo4, S. Papa1, M. Toigo5, C. Spengler1

1. Institute of Human Movement Sciences and Sport, Exercise Physiology Lab, ETH Zurich, Zurich, Switzerland. 2. Biosense Webster (Johnson & Johnson), Zug, Switzerland. 3. Novartis International AG, Basel, Switzerland. 4. Kieser Training AG, Zurich, Switzerland. 5. Balgrist University Hospital, Zurich, Switzerland.

Background: Muscle strength is influenced by muscle cross-sectional area (CSA) and fiber type composition. Especially in the elderly, it is unclear to which extent these muscle characteristics influence volitional and non-volitional muscle force. To address this, quadriceps twitch contractile properties prior to (pre) and after (post) a fatiguing knee-extension task were related to fiber type CSAs. Methods: Thirteen healthy, untrained elderly men (63.9±2.6 years) participated in the study and all agreed to a vastus lateralis biopsy to assess fiber-type specific CSAs. Total quadriceps muscle CSA (CSAQ) and fiber-type specific muscle CSA (CSAI and CSAII) were estimated by modeling thigh lean mass by means of a DXA scan. Potentiated quadriceps twitches were elicited by supramaximal magnetic femoral nerve stimulation before and immediately after fifty maximal, isokinetic knee extensions at 180o/s. Results: Significantly lower post-exercise values were observed in twitch amplitude (Qtw: pre 47.8±13.0, post 39.8±12.2 Nm, p<0.01), rate of torque development (RTD: pre 1416±645, post 1216±575 Nm s-1, p<0.05), relaxation rate (RR: pre -488.5±160.5, post -394.6±138.3 Nm s-1, p<0.01) and maximal voluntary torque (MVT: pre 183.5±38.9, post 167.2±33.0 Nm, p<0.001) while voluntary activation (VA: pre 88.9, post 86.6 %, p>0.05) remained unchanged. Single twitch characteristics pre exercise were not related to CSAQ, CSAI and CSAII, but pre-MVT showed a significant relationship with CSAQ (pre: r=0.73, p<0.05) as well as CSAII (r=0.71, p<0.05). Fatigue-related twitch characteristics, i.e. pre-to-post differences (Δ) in Qtw, RTD and RR, were significantly associated with CSAII: ΔQtw (r=-0.78, p<0.01), ΔRTD (r=-0.64, p<0.05) and ΔRR (r=0.77, p<0.01), while a trend was observed for ΔMVT (r=-0.51; p<0.1). A stepwise regression model to predict CSAII (dependent variable) including ΔQtw, ΔRTD, ΔRR andΔMVT as predictive parameters resulted in ΔQtw being the only significant predictor of CSAII (CSAII=-0.91*ΔQtw +17.25; both β<0.01, r2=0.58). Conclusion: The change in single twitch characteristics in an intense fatiguing task may potentially serve as a non-invasive tool to predict CSAII in untrained, elderly men.

Where applicable, experiments conform with Society ethical requirements