*3.2. Normality of EMG Variables of the LLM by CFI*

Table 2 shows the Shapiro–Wilk test results on the normality of the EMG variables of the LLM by CFI types for left and right curves in the simulator.

**Table 2.** Normality of the electromyography variables of the lower limb muscles for particular types of customized foot insoles for left and right curves in the simulator.


Abbreviations: EVA, ethylene vinyl acetate; Right curve, Knee touching the road; Left curve, Lower extremity towards the motorcycle body part. *p* Values are from Shapiro-Wilk tests

Intraclass Correlation Coefficient for EMG in LLM

Table 3 shows the ICC values for EMG activity in the LLM by CFI types for left and right turns in the simulator.

Table 4 shows the EMG activity patterns of the LLM by type of CFI for left and right curves in the simulator. Table 5 shows comparisons between pairs of CFIs on these activity patterns.

The selective aluminum (60 HB Brinell hardness) CFI generated statistically significant smaller amplitude peaks than Eva 52% and Polypropylene 58% CFIs compared with Standard EVA 25% CFI for left and right curves in the simulator (*p* < 0.001) in all muscles studied except for the fibularis longus right curve that is increased (*p* < 0.001).

In another hand, polypropylene 58◦ CFI produced statistically significant smaller amplitude peaks than Eva 52% CFI compared with Standard EVA 25% for left and right curves in the simulator for all muscles (*p* < 0.001) except also, for the fibularis longus right curve which increased (*p* < 0.001).

The results using Eva 52% are lower compared with Standard EVA 25% for left and right curves in the simulator for all muscles (*p* < 0.001) except for the fibularis longus right curve which increased (*p* < 0.001).

**Table 3.** Intraclass correlation coefficients, standard error of measurement and minimal detectable change for electromyography (EMG) activity patterns of the lower limb muscles by types of customized foot insoles for left and right curves in the simulator.


Abbreviations: 95% CI, 95% confidence interval; ICC, intraclass correlation coefficient; SEM: standard error of the mean; MDC: minimal detectable change; EVA, ethylene vinyl acetate; Right curve, Knee touching the road; Left curve, Lower extremity towards the motorcycle body part


**Table 4.** Maximum muscular activity of the lower limb muscles (LLM) as measured by EMG for di fferent customized foot insoles (CFI) for left and right curvesthesimulator.

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**Table 5.** Comparisons between types of customized foot insoles in terms of EMG activity of the lower limb muscles for left and right curves in the simulator.

Abbreviations: SD: standard deviation; 95% CI: 95% confidence interval; EVA, ethylene vinyl acetate; Right curve, Knee touching the road; Left curve, Lower extremity towards the motorcycle body part

## **4. Discussion**

Researchers have carried out several investigations on EMG activity patterns of LLM during cycling [36–38]. Notably, Bousie et al. [36] found that contoured insoles increased the contact area of the foot in stationary cycling. In addition, Casado et al. reported variations in motorcycle riders' plantar pressures with different CFIs when riding in a motorcycle simulator, concluding that metatarsal and hallux pressures decreased with the hardest CFI [17].

Riding on a speed circuit with multiples curves and bends requires precise control of the dynamics of the supersport motorcycle. Stability on the motorcycle is achieved with the hands on the handlebars, buttocks on the seat, legs, and feet on the footpegs. Motorcycle riders perform load transfers during changes in speed, lateral tilts on curves, and changes in direction, demanding repeated physical effort [39,40].

To our knowledge, our investigation is the first to use EMG for recording the muscular activity of the LLM in motorcycling with different CFI. We evaluated the effects of four types of CFI: (1) only polypropylene (58◦ Shore D), (2) selective aluminum (60 HB Brinell hardness) in the metatarsal and first hallux areas and polypropylene elsewhere (58◦ Shore D), (3) ethylene vinyl acetate (EVA) (52◦ Shore A), and (4) standard EVA (25◦ Shore A; used as control).

In our research, we studied the variation of EMG activity peak amplitudes in the right lower leg of each rider taking right and left curves as they used different CFIs. To maintain the stability of the motorcycle when taking a curve, a rider touches the road on the inner part of the curve with his knee and applies force against the footpeg with the plantar aspect of his first metatarsal bone. When taking the curve, the rider also moves his other leg toward the body of the motorcycle. The fibularis longus is the main muscle that keeps the first metatarsal bone in plantarflexion against the footpeg and therefore is one of the most important muscles for maintaining stability as the knee touches the road during the curve.

The select aluminum CFI had significantly smaller amplitude peaks than the other CFIs for both left and right curves in the simulator for the tibialis anterior, gastrocnemius lateralis, gastrocnemius medialis, soleus, and fibularis brevis. For the fibularis longus, the select aluminum CFI had significantly smaller amplitude peaks than other CFIs in left curves, but significantly higher amplitude peaks than other CFIs in right curves. We suspect that the high activity of the fibularis longus in right curves, when the knee touches the road, increases stability while riding. Also, decreased activity of the other LLM in left and right curves would likely contribute to decreased fatigue when riding.

More studies are needed on muscular activity during sport motorcycling because there are currently speed circuits with a greater number of right and left curves than in the circuit our riders rode. The data we obtained would help estimate the overloading of LLM in such contexts.

A limitation of our study is the lack of inertial forces and steering control challenges in our simulator that occur when riding a motorcycle on a real speed circuit. Further research is needed on the physical effects of motorcycling during actual sport races.
