Voluntary activation failure is detectable in some myositis patients with persisting quadriceps femoris weakness: an observational study

Table 3 The muscle strength, disease activity and damage scores, and twitch interpolation results of patients with myositis

QF (MVC) Strength category	Patient number	QF mass-normalised force F/LBM (N/kg)	Activity status	Damage score (0–3)	Twitch status (-/+)
"Not weak"	1	8.83	Inactive	0	-
	2	7.17	Active -	1	-
	4	5.64	Active -	1	-
	5	5.63	Inactive	1	-
	6	5.40	Inactive	1	-
	3	6.40	Inactive	2	+
"Weak"	7	4.14	Active -	1	-
	8	3.97	Active -	1	-
	9	3.69	Active	1	-
	11	2.82	Active	1	-
	12	2.28	Inactive	3	-
	14	2.10	Active	1	-
	*17	1.30	Active	3	-
	*19	0.99	Inactive	3	-
	10	3.32	Active	1	+
	13	2.11	Active -	2	+
	15	1.84	Active -	3	+
	16	1.76	Active -	1	+
	18	1.00	Active +	2	+
	20	0.80	Inactive	3	+

Twenty patients with myositis listed according to their mass-normalised strength and twitch interpolation results, and stratified as "not weak" and "weak" according to their F/LBM results (see text). In general terms, as QF strength decreased, the incidence of positive twitches increased. Cases 17 and 19 had had muscle biopsies within the previous 6 months, and the results showed end-stage disease with severe muscle atrophy and fibrosis. F/LBM, force per units of lean body mass; MVC, maximum voluntary contraction; QF, quadriceps femoris.

ISSN: 1478-6362