Tubular member and tennis racket

A tubular member adapted for a partial structure of a piece of sports equipment used for striking a ball, comprising:

• an inner frame portion extending in a first axial direction, said inner frame portion including a first inner frame section, a second inner frame section, and an inner connecting section that interconnects said first inner frame section and said second inner frame section;
• an outer frame portion extending in said first axial direction and spaced apart from said inner frame portion in a second axial direction that is perpendicular to said first axial direction, said outer frame portion including a first outer frame section, a second outer frame section, and an outer connecting section that interconnects said first outer frame section and said second outer frame section;
• a wide portion extending in said first axial direction and extending straightly from said outer frame portion to said inner frame portion in said second axial direction;
• and
• a narrow portion extending in said first axial direction and interconnecting said inner frame portion and said outer frame portion, said narrow portion being arc-shaped and spaced apart from said wide portion in a third axial direction that is perpendicular to said first axial directions and said second axial direction, a length of said wide portion in said second axial direction being equal to a first width, a length of said narrow portion in said second axial direction being equal to a second width, said second width being smaller than said first width, said first inner frame section having a first inner side end that is connected to said wide portion and a first inner connecting end that is opposite to said first inner side end, said second inner frame section having a second inner side end that is connected to said narrow portion and a second inner connecting end that is opposite to said second inner side end, said inner connecting section interconnecting said first inner connecting end and said second inner connecting end, said first outer frame section having a first outer side end that is connected to said wide portion and a first outer connecting end that is opposite to said first outer side end, said second outer frame section having a second outer side end that is connected to said narrow portion and a second outer connecting end that is opposite to said second outer side end, said outer connecting section interconnecting said first outer connecting ends and said second outer connecting end, a plane that is perpendicular to said second axial direction and that passes through said wide portion and said narrow portion being defined as a reference plane, starting from said first inner side end, said first inner frame section extending gradually away from said reference plane to said first inner connecting end, starting from said second inner connecting end, said second inner frame section gradually approaching said reference plane to reach at said narrow portion, starting from said first outer side end, said first outer frame section extending gradually away from said reference plane to said first outer connecting end, starting from said second outer connecting end, said second outer frame section gradually approaching said reference plane to reach at said narrow portion, a maximum distance between an edge of said inner connecting section distal from said outer connecting section and an edge of said outer connecting section distal from said inner connecting section in said second axial direction being equal to a third width, a ratio of said third width to said first width being 11:9, each of a radius of curvature of a portion of said first inner frame section that is adjacent to said wide portion and a radius of curvature of a portion of said first outer frame section that is adjacent to said wide portion ranging from 71 millimeters to 86 millimeters, each of a radius of curvature of a portion of said second inner frame section that is adjacent to said narrow portion and a radius of curvature of a portion of said second outer frame section that is adjacent to said narrow portion ranging from 20 millimeters to 25 millimeters, a length of said tubular member in said third axial direction being equal to a section length, a ratio of said section length to said first width being 25:9, a radius of curvature of said narrow portion ranging from 2.7 millimeters to 3.3 millimeters.