1 Introduction

As a role of rehabilitation for joint diseases, walking necessary for early social reintegration and reacquisition of lower limb muscle activity are indispensable. Postoperative patients such as lower limb bone fracture, total knee arthroplasty (TKA), total hip arthroplasty (THA), etc. are accompanied by surgical invasion and long-term bedding, and single joints that are considered to be anti-gravity muscles compared with bipartite muscles Muscle contraction of the muscle is remarkable, and selective training of a mono-articular muscle is also an important matter of a physical therapist. However, knee joint extension movement with weight load applied to the distal end of the lower limb at the sitting posture, which is performed as a voluntary training other than training time, causes excessive contraction in the rectus femoris muscle (RF), a bipartite muscle It is difficult to say that it is effective as a selective training of the medial vastus muscle (VM), which is a mono-articular muscle, as voluntary training to be performed by the patient himself.

To solve this problem, we modeled the musculoskeletal system of the human being with a single articulated muscle and a bi-articular muscle [1], and utilize the output direction control characteristic [2] clarifying the relationship between the output distribution of the lower limb tip and each muscle activity It has been suggested that it can be applied to selective strength training [3, 4]. Using this output direction control characteristic, we developed a selective training device for the lower extremity mono-articular muscle which patients can use as self-training in rehabilitation [5], aimed at actual use after clinical evaluation In this case, since we used the device for patients who are actually hospitalized for social rehabilitation and carried out the confirmation of the effect, we report on it.

2 Development of Selective Training Device for Lower Extremity Mono-articular Muscle

2.1 Output Direction Control Characteristics of Lower Limb

According to the output direction control characteristic by Kumamoto et al. [4], when extending the lower limb from the posture shown in Fig. 1, if exercising at the maximum effort of 30 to 40% or more is done, the hip joint single muscle group In the activity, the direction of the lower thigh axis (C), the direction connecting the ankle joint and the hip joint (B) in the activity of the knee joint mono-articular muscle group, the direction parallel to the thigh axis in the activity of the femoral bi-articular muscle group (A).

Fig. 1.
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Output direction control characteristics

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By utilizing this characteristic, if the output direction and the load amount can be set by the device, each muscle group of the lower limb can be selectively trained.

2.2 The Developed Lower Limb Mono-Articular Muscle Training Machine

As shown in the previous section, we think that it is possible to selectively train active muscle groups by arbitrarily adjusting the extension direction (angle) of the lower limbs. Therefore, we prepared a device that can be used by the patient at the bed end sitting position or the wheelchair sitting position, and furthermore, the output direction can be adjusted.

Figure 2 shows the configuration of the training device developed this time. The guide shown in this figure is for determining the direction of extension of the lower limbs, and it is possible to adjust the height and angle of the guide.

Fig. 2.
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Selective training device

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The loading amount was made to be able to be worn through a dedicated belt with a rubber band that is frequently used clinically. As a result, consideration has been given so that the rehabilitation staff can adjusted sensuously. Figures 3(a), (b) and (c) show a rubber band, the fixing belt, and the state where the rubber band and the belt are attached to the waist respectively.

Fig. 3.
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(a) A rubber band, (b) The fixed belt, (c) A state of wearing the belt on the waist.

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Figure 4 shows the state of the developed device and the load applied to the lower limbs, that is, the state before starting the training at the wheelchair sitting position.

Fig. 4.
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Examples of using the developed device.

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In order to maximize the effect of this device, it is important to adjust the angle of the guide by the rehabilitation staff. In order to minimize the vector component in the direction A caused by the activity of the bipartite muscle shown in Fig. 1, it is necessary to determine the output in the direction C. However, this matter shows the activity of a mono-articular muscle in the knee joint Since the vector component in the B direction decreases, it is reasonable to decide the output between the B direction and the C direction. Therefore, when determining the output angle, the rehabilitation staff palpates the rectus femoris muscle (RF), which is the bipartite muscles of the thigh, and the medial vastus muscle (VM), which is the mono-articular muscle of the knee joint, and the muscle activity It is desirable to adjust the angle of the guide from the state.

3 Verification of Effect of Developed Device

3.1 Measurement Method of Muscle Activity

In this study, with the approval of Matsuyama City Rehabilitation Hospital Ethics Committee, subjects fully explained the research and obtained consent to the subjects. Subjects were 1 patient with THA postoperative without any neurological disease who was hospitalized at Matsuyama Rehabilitation Hospital recovery hospital. The EMG master used was EMG Master (manufactured by Ozawa Medical Instrument Co., Ltd.), sampling frequency was set to 1 kHz, and the electrode pasting site was treated with sufficient skin, then recommended by Shimono [6].

Assuming 40 [%] of the maximum effort for both loads, we perform integral EMG (IEMG) analysis in the middle 3 s when holding at the final limb position for 5 s to obtain the muscle activity amount. The desired active muscle group is the medial broad muscle (VM) and rectus femoris muscle (RF). The effectiveness of selective training was verified by dividing VM muscle activity amount during training by RF muscle activity amount and calculating VM/RF value. If the VM/RF value shows a high value, this means that RF muscle activity is suppressed.

3.2 A Comparative Experiment of the Muscle Activity Amount with Respect to the Output Angle

As a preliminary experiment, we perform an experiment to find the optimum output angle (θ [rad] in the figure). As a selective training, use the device developed at the sitting position as shown in Fig. 5, and carry out the knee joint extension movement along the guide. At that time, 10° of flexion of the knee joint was taken as the final limb position.

Fig. 5.
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Selective training with developed apparatus.

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The output angle (θ) of selective training is determined by using IEMG analysis. The output angle is measured in four stages of 0 [rad] in the horizontal direction and π/12 [rad], π/6 [rad], π/4 [rad] in the downward direction. The VM and RF muscle activity ratios of each angle with respect to the muscle activity amount of output angle 0 [rad] are obtained by dividing the muscle activity amount of each output angle in VM and RF by the muscle activity amount of output angle 0 [rad]. Moreover, by comparing with the VM/RF value, we confirm the change of the muscle activity amount at the output angle and investigate the optimum output angle.

3.3 Comparative Experiment with Conventional Training Method

Figure 6 shows the weight load training method that has been practiced in clinical practice. This method is an extension movement from π/2 [rad] flexion position of the knee joint in which the weight load is added to the distal end of the lower leg at the side sitting position.

Fig. 6.
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Traditional weight type training.

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4 Results

4.1 Selection of Optimum Output Angle

By the selective training method shown in Fig. 5, the activity amount of the mono-articular muscle (VM) and the bipartite muscle (RF) with respect to the output angle was measured. Figures 7 and 8 show the integrated EMG of VM and RF when the output angle (θ) is π/4 [rad]. The horizontal axis of the figure is 3 s measured at 1 [kHz], and the vertical axis is the myoelectric potential [mV]. The RMS value of the VM was 0.012 [mV], and the RF was found to be 0.010.

Fig. 7.
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Output of π /4 [rad] direction of mono-articular muscle group.

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Fig. 8.
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Output of π /4 [rad] direction of bipartite muscle group.

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Similarly, Table 1 shows the result of integrating electromyogram analysis in each output direction. The muscle activity ratio and the VM/RF value in the case where the muscle activity amount in the 0 [rad] direction which is the maximum value is 100 are shown.

Table 1. Muscle activity amount per output direction
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It was found that VM, RF muscle activity rate and VM/RF value tended to decrease with increase of output angle in selective training. The higher the VM/RF value, the more selective training effect is shown. Therefore, an output angle of 0 [rad] with a higher VM/RF value and the highest muscle activity rate of VM is determined as an optimum angle.

4.2 Effectiveness Verification of Selective Training

Table 2 shows the selective training at the output angle 0 [rad] determined in the previous section (Fig. 5) and the muscle activity amount and VM/RF value of the conventional type of weight load training (Fig. 6). It can be seen that the amount of activity of the VM in the conventional training method is larger than that of the selective training method and the RF activity is also very large. However, the VM/RF value is 0.44 for the weight load training and 1.62 for the selective training. In other words, by training with the optimum output angle using the selection training device produced this time, it was about 4 times higher than the conventional method.

Table 2. Effect of selective training.
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5 Discussion

Figure 9 shows VM/RF values at four output angles of the selective training method and the VM/RF value in conventional weight load training. The change in VM/RF value for each output angle shown in the same figure is similar to the tendency of the execution muscle force in the output direction of the lower limb tip for the healthy persons of Oshima et al. [1, 2] and the lower limb output direction. We believe that regulation of lower limb output direction is effective as selective training of muscle fr this postoperative patient. On the other hand, in order to suppress the vector in direction A shown in Fig. 1 which occurs during RF activity, we considered that it is effective to adjust the output angle in the C direction. However, in the case of 0 [deg] indicating B direction, the output angle became optimum. This is considered to be due to the fact that the decrease in the muscle activity rate of VM was marked more than the RF in this case with the increase of the output angle.

Fig. 9.
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VM/RF activity rate against difference in output angle.

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In addition, the VM/RF value shows a high value at all output angles of selective training compared with the value of the conventional weight load training. The weight load training compared in this study seems to have promoted the muscle activity of RF, because the initial motion output includes many vector components in direction A shown in Fig. 1. Especially postoperative patients who are forced to stay in bed for a long period of time, VM’s muscle contraction tends to be more pronounced, I believe that it is partly due to the fact that who are difficult to activate VMs.

On the other hand, many users intuitively understand the convenience of weight load training considering preparation time and storage place. Therefore, although the developed selective training device has an advantage as an effect, it is thought that it is necessary to improve against the convenience of the user. Devices that are not used in the clinical setting have no existential value and can not be neglected to listen to the user’s voice in developing the device.

6 Conclusions

In this study, compared with the weight load training, we confirmed the effect of selective training of the lower limb mono-articular muscle in hospitalized patients using the developed device. As a result, I got the following conclusion.

  1. (1)

    By using the device developed this time, the patient can be used in the bed end sitting position or the wheelchair sitting position, and the output direction can be adjusted to make the unipolar muscle group dominate over the bipartite muscle group.

  2. (2)

    In postoperative patients who are forced to lie longer for a long time, the VM/RF tends to decrease as the output angle (θ [rad] in Fig. 5) increases.

  3. (3)

    From the conventional weight load training, the VM/RF value becomes higher when the selective training method using the developed device is used. That is, the activity of the mono-articular muscle group can be made larger than the activity of the bipartite muscle group.