Reduced Neuromuscular Performance in Night Shift Orthopedic Nurses: New Insights From a Combined Electromyographic and Force Signals Approach

The effect of sleep–wake rhythm disruption on neuromuscular control and muscle

fatigue has received little attention. Because nurse shift work is so varied, including

overnight duty, rotating shift schedules, early awakening, and interrupted nocturnal

sleep, it offers an interesting model to study this paradigm. It has been investigated

so far using only subjective markers. A combined approach based on the simultaneous

analysis of surface electromyographic (sEMG) and force signals can objectively detect

possible deficits in neuromuscular control and muscle fatigue. With this study we

investigated neuromuscular activation and muscle contraction capacity at submaximum

and maximum level in nurses working two night-shift schedules and compared them to

levels in nurses working entirely in day shifts. Sleep quality and activity levels were also

assessed. The study sample was 71 nurses grouped by their shift work schedule: night

shift for 5 days (NS5, n = 46), night shift for 10 days (NS10, n = 9), and only day/swing

shift (DS, n = 16). Before and after the shift-work cycle, maximum voluntary contraction

(MVC) force and muscle activation, neuromuscular control, and muscle fatigability were

measured in the finger flexor muscles. Activity level and sleep quality during the shiftwork

cycle were recorded with a wrist actigraph. After the shift-work cycles, MVC force

and muscle activation were decreased (􀀀11  3% and 􀀀33  3%, p < 0.001) as

was neuromuscular control (􀀀36  8%, p = 0.007), whereas muscle fatigability was

increased (C 19  9%, p = 0.006) in the NS5 and the NS10 group. Sleep quality was

lower in the NS5 and the NS10 group (􀀀8  1.8% and 􀀀15%3, respectively, p < 0.001),

while the activity level for the three groups was similar. There was a clear reduction

in neuromuscular control and an increase in muscle fatigue in the nurses working the

night shift. These findings may inform of work schedule planning or recommendations

for devising new recovery strategies to counteract neuromuscular alterations in night

shift nurses.