Table 3.

Comparison of main features of lower limb fatigue resistant strategies

Fatigue strategy	Muscle fatigue definition	Fatigue metric	Muscle group	Stimulation strategies & electrodes	Subjects	Results
Popovic et al. 2009 [63]	70 % decrease of max torque	Fatigue Interval	Quadriceps	Synchronous single electrode vs Asynchronous 4 smaller electrodes	6 complete SCI patients	150 % increase of fatigue interval with electrode array
Malesevic et al. 2010 [58]	70 % decrease of max torque	Fatigue Interval	Quadriceps	Synchronous single electrode vs Asynchronous 4 smaller electrodes	6 complete SCI patients	Synchronous: 31 % increase of post-therapy muscle fatigue resistance.
				20 daily sessions		Asynchronous: 4 % increase of post-therapy muscle fatigue resistance.
Nguyen et al. 2011 [64]	Torque decrease of 3 dB	Fatigue Index, Fatigue Time, Torque-Time-Interval	Tricep Surae	Synchronous single electrode vs Asynchronous 4 smaller electrodes	1 complete SCI	Asynchronous stimulation: higher torque values for a longer period of time
Sayenko et al. 2013 [67]	Torque decrease of 3 dB	Fatigue Index	Knee flexors/extensors, plantar flexor/dorsiflexor	Synchronous single electrode vs Asynchronous 4 smaller electrodes	15 able-bodied subjects	Asynchronous stimulation higher fatigue resistant than synchronous
Sayenko et al. 2014 [65]	They studied muscle contraction properties	Torque-Rise Time, Rate of torque development, Half-Relaxation-Time, Rate of torque relaxation	Tricep Surae, right gastrocnemius	Synchronous single electrode vs Asynchronous 4 smaller electrodes	15 able-bodied subjects	Amplitude of M-waves depends on the location of the stimulated pad electrodes. Peaks on M-waves on ascending phase of synchronous stimulation are fused as fatigue occurs.