ch = 0;
if (sprite_index == spr_muscbul1 && ch == 0)
{
    sprite_index = spr_muscbul2;
    ch = 1;
}
if (sprite_index == spr_muscbul1_r && ch == 0)
{
    sprite_index = spr_muscbul2_r;
    ch = 1;
}
if (sprite_index == spr_muscbul2 && ch == 0)
{
    sprite_index = spr_muscbul1;
    ch = 1;
}
if (sprite_index == spr_muscbul2_r && ch == 0)
{
    sprite_index = spr_muscbul1_r;
    ch = 1;
}
alarm[0] = flexspeed;
if (offset == 1)
    vspeed = -4;