d
\(\underset{\begin{smallmatrix} 
 stored\,\,in \\ 
 the\,\,form\,\,of\,\,\downarrow  
 \\ 
 Glycogen 
\end{smallmatrix}}{\mathop{Glu\cos e}}\,\,\xrightarrow[\begin{smallmatrix} 
 (does\,\,not\,\,need\,\,oxygen; \\ 
 enzymes\,\,are\,\,need\,\,only) 
\end{smallmatrix}]{1}\)

\(\underset{\underset{Lactic\,\,acid}{\mathop{\downarrow }}\,}{\mathop{Pyruvic\,\,acid}}\,\xrightarrow{{{O}_{2}}}C{{O}_{2}}\,+\,{{H}_{2}}O\)

During vigorous exercise suffcient oxygen is not available to meet the energy demand so, energy is derived through conversion of pyruvic acid to lactic acid.