diff --git a/src/ast.ts b/src/ast.ts
index 88f1786..2288481 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -7,12 +7,9 @@ export type Workout = {
   intervals: Interval[];
 };
 
-export type IntervalData = {
+export type Interval = {
+  type: IntervalLabelTokenValue;
   duration: number;
   power: { from: number; to: number };
   cadence?: number;
 };
-
-export type Interval = IntervalData & {
-  type: IntervalLabelTokenValue;
-};
diff --git a/src/parser.ts b/src/parser.ts
index 75421e0..c51c720 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -1,11 +1,7 @@
-import { Interval, IntervalData, Workout } from "./ast";
+import { Interval, Workout } from "./ast";
 import { isIntervalLabelTokenValue, Token } from "./tokenizer";
 
-type Header = {
-  name?: string;
-  author?: string;
-  description?: string;
-};
+type Header = Partial<Omit<Workout, "intervals">>;
 
 const extractText = (tokens: Token[]): [string, Token[]] => {
   let text;
@@ -49,6 +45,8 @@ const parseHeader = (tokens: Token[]): [Header, Token[]] => {
   return [header, tokens];
 };
 
+type IntervalData = Omit<Interval, "type">;
+
 const parseIntervalParams = (tokens: Token[]): [IntervalData, Token[]] => {
   const data: Partial<IntervalData> = {};