The student has seen being physically fit as an end rather than the means (that / which) we know it to be.
1 has seen (现在完成时)--------应该改写成 sees --------解释为“认为”,所以“一般现在时”更好.
2 the means that / which we know it to be(定语从句部分)--------know是一般现在时,用对了.
3 the means that / which（that / which 是连接词,指代the means,做宾语补足语的一部分） we (主语)know（谓语） it （宾语）to be（宾语补足语的一部分）
4 we (主)know （谓）it （宾）to be a means （宾补）== we know that it is a means (这是宾语从句)