In this study, a low-cost, wireless, and smartphone-controlled surface electromyography (EMG) system was designed and developed for consumers, and the recorded EMG signals were evaluated against a reference laboratory EMG system during fatiguing contraction. Using commercially available inexpensive components, the components of the EMG signal-acquisition circuit were optimized, and a microcontroller was combined with a Bluetooth module. The EMG signals were then converted from analog to digital signals and transmitted to a smartphone via Bluetooth serial communication. EMG signals from the biceps brachii of six healthy subjects were recorded separately using two EMG systems during sustained submaximal isometric contraction until the endurance limit was reached. The root mean square (RMS) and mean power frequency (MPF) of the EMG signals were calculated. The results indicated that both the EMG systems exhibited a characteristic progressive increase in EMG RMS and decrease in EMG MPF during sustained isometric contraction. The relative agreement between the two EMG systems, assessed by intraclass correlation coefficient (ICC), was excellent for EMG RMS (ICC 0.933, P < 0.001) and moderate for EMG MPF (ICC 0.662, P = 0.049). The cost of the sensor components in the hardware was ¥8,486 per unit. The proposed consumer-friendly EMG system, which is inexpensive and highly versatile in terms of wireless and smartphone accessibility, can detect the phenomenon associated with increased amplitude and low-frequency components during muscle fatigue contraction with a magnitude similar to that of the commercially available laboratory EMG systems.

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From a biomechanical viewpoint, no longitudinal quantitative studies have been conducted on inexperienced paddlers. The present study aimed to investigate changes in three-dimensional paddling kinetics and kinematics, whole-body kinematics, and muscle activity with four-week on-water kayak training in a novice paddler. The participant practiced kayak paddling on river for four weeks. Before and after training, paddling kinetics and kinematics, body kinematics, and electromyography (EMG) activity were measured using a kayak ergometer. After the four-week training, the time required for on-water paddling for 270 m was reduced by 7.3% from pre to post training, while the average impulse in the x-direction significantly (P &lt; 0.001, partial eta squared [η2] = 0.82) increased from 71.9 ± 1.9 to 91.1 ± 5.4 N kg−1 s−1. Furthermore, with training, the stroke rate and stroke length in the x-direction significantly (P &lt; 0.001, partial η2 = 0.80 and 0.79, respectively) increased from 62.8 ± 1.2 to 81.0 ± 2.9 spm and from 1.53 ± 0.04 to 1.71 ± 0.02 m, respectively. After training, the transition time significantly (P &lt; 0.001, partial η2 = 0.32) decreased (from 0.04 ± 0.01 to 0.01 ± 0.01 s), and there was an increase in paddle catch position (from −0.88 ± 0.01 to −1.04 ± 0.03 m). The pull time was not significantly changed (P = 0.077, partial η2 = 0.08) because of the increasing stroke length after training, meaning that substantial pull time, which defined as pull time relative to the stroke displacement, was shorter in post-training than in pre-training. The relative change in average impulse in the x-direction with training was significantly (r = 0.857, P = 0.014) correlated with that of vastus lateralis EMG. These results indicated that after four-week kayak training of the novice paddler, the key mechanism underlying time reduction to perform on-water paddling for 270 m was associated with (1) increased average impulse along the propulsive direction caused by an increase in vastus lateralis EMG and (2) a higher stroke rate, which was attributed to a reduction in the pull and transition times.