Are muscle weakness and falls status really correlated in physically active women?

1A comment to Crozara et al. Isokinetics and Exercise Science 24(1): 67–77, 2016. (2016). ∗Corresponding author: Thomas Cattagni, University of Nantes, Laboratory “Movement, Interactions, Performance” (EA 4334), 25 bis boulevard Guy Mollet, BP 72206, 44322 Nantes Cedex 3, France. E-mail: [email protected]. Second, the authors observed no difference in plan26 tarflexors (PF) co-contraction during maximal isoki27 netic dorsiflexion between young and older groups 28 while most of the studies reported a decreased PF 29 coactivation/co-contraction with aging [3–5]. Beyond 30 the potential effect of the contraction types (i.e. isoki31 netic herein vs. isometric in the aforementioned stud32 ies), other methodological considerations might ex33 plain this discrepancy. First, Crozara and colleagues 34 estimated the PF co-contraction level by comparing 35 the EMG amplitude measured during maximal dor36 siflexion between PF and dorsiflexors (DF). Other 37 authors compared the PF EMG amplitude measured 38 during maximal dorsiflexion with PF EMG during 39 maximal plantarflexion to estimate the level of PF 40 coactivation/co-contraction [3–5]. Second, the choice 41 of the lateral gastrocnemius muscle (LG) to represent 42 the PF muscles is questionable. As LG accounts for 43 only 17–18% of the triceps surae volume [6] and that 44 triceps surae contribution to the total plantarflexion 45 moment ranges from ∼ 65% [7] to > 88% [8], we con46 tend that LG cannot be considered as representative of 47 the PF muscles. Finally, the three muscles of the tri48 ceps surae are differently altered by aging. Although 49 LG relative volume (% of the total triceps surae vol50 ume) is stable through the age, an increase and a de51 crease in relative volume is observed for the soleus and 52 the MG muscle, respectively [6]. In other words, a sim53 ilar change in co-activation among these three muscles 54 will not produce a similar mechanical effect in terms of 55 force production. This highlights the need of assessing 56 each of these muscles to provide a complete picture of 57 change in their behavior with aging. 58