IEEE Consumer Electronics Magazine - January/February 2020 - 55

& MUSCLE

IMBALANCE IS common during sports
or long-distance running and is a primary cause
of sports injury. By attempting to address these
injuries, "smart" sport aids have garnered considerable attention. Such devices record a range
of data, including a user's movement, heart rate,
and cadence.
Although sensors that quantify and record
human movement and muscle firing patterns are
relatively common in kinesiology research, these
devices should provide more advanced functional applications such as biofeedback.
Vibration, or vibrotactile feedback, is a system
that creates a mechanical stimulus from an oscillatory motion. This mechanical stimulus at low
amplitudes and frequencies has been hypothesized to be a safe and effective way to facilitate
muscle contraction. This type of feedback has
advantages over other types, such as the electrotactile system, which can cause pain and fatigue,
and force feedback, which can be cumbersome
and restrict a user's movement.1 Another finding
suggests that this type of vibration can be used as
an effective exercise intervention for enhancing
the neuromuscular performance of athletes.2
In rehabilitation, vibrotactile feedback is replacing functional electrical stimulation to remove the
dependence on visual monitoring of paraplegic
patients. A new wireless vibrotactile feedback system, the "TactaPack," developed by Lindeman
et al. in 2006, aimed to help patients recovering
from joint replacement surgery. The TactaPack
vibrates as a warning to patients when the kinematic reading from patients exceeds a threshold
value.3 Moreover, this type of feedback has been
used in stroke rehabilitation to deliver vibration
feedback on a corresponding leg when it collides
with virtual or real objects.
In terms of consumer healthcare, which is
focused on empowering consumers to self-manage their health,4 this smart knee brace embedded with vibration feedback is crucial to
monitor and alert the user when they have muscle activation abnormality at the knee.
Currently, no device can measure lower body
muscle activation during exercise while providing appropriate warnings. The knee relies on
the VMO and VL muscles for coordination, stability, and posture. Electromyography (EMG) signals provide vital information obtained through

January/February 2020

physiological measurements that can be used to
determine muscle strength and user movements.
In a previous study, processed EMG signals were
used to control the synchronization of mechanical instruments that replaced humans in task
performance.5
Under normal circumstances, the VL/VMO
activity ratio is approximately 16 and does not differ between males and females.7 Moreover, the
neuromuscular imbalance between the VL and
VMO can cause abnormal lateral tracking of the
patella, which can lead to a decrease in the activation of the VMO. Clinical solutions for increasing
the activation and thus the strength of the VMO
have been continuously addressed.8, 9
Recognizing that EMG signals can be used to
assess the strength of the VL and VMO, we developed a device to identify abnormal knee movement and initiate vibration feedback to alert
users to stop the abnormal movement. This
device can help users avoid sports injuries.
Real-time processing of user EMG data enables our device to immediately detect abnormal
muscle statuses and emit vibrations that alert
users regarding the risk of muscle injury. To
describe the algorithm used to allow the judgment of muscle imbalance between VL and VMO
and the hard-ware development containing a
controlled vibration module which will be necessary for a smart knee brace, this study developed a prototype of a smart knee brace by
developing the algorithm used to allow the judgment of muscle imbalance between VL and VMO
and the integrated hardware containing a controlled vibration module.

MATERIALS AND METHODS
Subject
Two healthy subjects (age ¼ 28 Æ 8 years old,
height ¼ 170 Æ 3 cm, weight ¼ 65 Æ 3 kg) free of
any musculoskeletal pathology that might interfere with the kinematics or kinetics of the upper
and lower extremities participated in this study.
Equipment
Wireless EMG sensors were obtained from
Delsys, Inc. (TrignoTM , Delsys, Inc., Natick, MA,
USA). EMG sensors were placed on the VL and
VMO on each side of the body. Two

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