diff --git a/src/ast.ts b/src/ast.ts
index fc20753..88f1786 100644
--- a/src/ast.ts
+++ b/src/ast.ts
@@ -1,3 +1,5 @@
+import { IntervalLabelTokenValue } from "./tokenizer";
+
 export type Workout = {
   name: string;
   author: string;
@@ -5,9 +7,12 @@ export type Workout = {
   intervals: Interval[];
 };
 
-export type Interval = {
-  type: "Warmup" | "Cooldown" | "Interval" | "Rest";
+export type IntervalData = {
   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 c5d164d..1739a70 100644
--- a/src/parser.ts
+++ b/src/parser.ts
@@ -1,5 +1,5 @@
-import { Interval, Workout } from "./ast";
-import { LabelTokenValue, Token } from "./tokenizer";
+import { Interval, IntervalData, Workout } from "./ast";
+import { isIntervalLabelTokenValue, Token } from "./tokenizer";
 
 type Header = {
   name?: string;
@@ -25,23 +25,17 @@ const parseHeader = (tokens: Token[]): [Header, Token[]] => {
 
   while (tokens[0]) {
     const token = tokens[0];
-    if (token.type === "label" && token.value === LabelTokenValue.Name) {
+    if (token.type === "label" && token.value === "Name") {
       tokens.shift();
       const [name, rest] = extractText(tokens);
       header.name = name;
       tokens = rest;
-    } else if (
-      token.type === "label" &&
-      token.value === LabelTokenValue.Author
-    ) {
+    } else if (token.type === "label" && token.value === "Author") {
       tokens.shift();
       const [author, rest] = extractText(tokens);
       header.author = author;
       tokens = rest;
-    } else if (
-      token.type === "label" &&
-      token.value === LabelTokenValue.Description
-    ) {
+    } else if (token.type === "label" && token.value === "Description") {
       tokens.shift();
       const [description, rest] = extractText(tokens);
       header.description = description;
@@ -55,8 +49,60 @@ const parseHeader = (tokens: Token[]): [Header, Token[]] => {
   return [header, tokens];
 };
 
+const parseIntervalParams = (tokens: Token[]): [IntervalData, Token[]] => {
+  const data: Partial<IntervalData> = {};
+
+  while (tokens[0]) {
+    const token = tokens[0];
+    if (token.type === "duration") {
+      data.duration = token.value;
+      tokens.shift();
+    } else if (token.type === "cadence") {
+      data.cadence = token.value;
+      tokens.shift();
+    } else if (token.type === "power") {
+      data.power = { from: token.value, to: token.value };
+      tokens.shift();
+    } else if (token.type === "power-range") {
+      data.power = { from: token.value[0], to: token.value[1] };
+      tokens.shift();
+    } else {
+      break;
+    }
+  }
+
+  if (!("duration" in data)) {
+    throw new Error("Duration not specified");
+  }
+  if (!("power" in data)) {
+    throw new Error("Power not specified");
+  }
+
+  return [data as IntervalData, tokens];
+};
+
 const parseIntervals = (tokens: Token[]): Interval[] => {
-  return [];
+  const intervals: Interval[] = [];
+
+  while (tokens[0]) {
+    const token = tokens.shift() as Token;
+    if (token.type === "label" && isIntervalLabelTokenValue(token.value)) {
+      const [{ duration, power, cadence }, rest] = parseIntervalParams(tokens);
+      intervals.push({
+        type: token.value,
+        duration,
+        power,
+        cadence,
+      });
+      tokens = rest;
+    } else if (token.type === "text" && token.value === "") {
+      // Ignore empty lines
+    } else {
+      throw new Error(`Unexpected token [${token.type} ${token.value}]`);
+    }
+  }
+
+  return intervals;
 };
 
 export const parse = (tokens: Token[]): Workout => {
diff --git a/src/tokenizer.ts b/src/tokenizer.ts
index 6e2cb67..04e47bd 100644
--- a/src/tokenizer.ts
+++ b/src/tokenizer.ts
@@ -1,12 +1,25 @@
-export enum LabelTokenValue {
-  Name = "Name",
-  Author = "Author",
-  Description = "Description",
-  Warmup = "Warmup",
-  Rest = "Rest",
-  Interval = "Interval",
-  Cooldown = "Cooldown",
-}
+export type HeaderLabelTokenValue = "Name" | "Author" | "Description";
+export type IntervalLabelTokenValue =
+  | "Warmup"
+  | "Rest"
+  | "Interval"
+  | "Cooldown";
+export type LabelTokenValue = HeaderLabelTokenValue | IntervalLabelTokenValue;
+
+export const isHeaderLabelTokenValue = (
+  value: string
+): value is HeaderLabelTokenValue => {
+  return ["Name", "Author", "Description"].includes(value);
+};
+export const isIntervalLabelTokenValue = (
+  value: string
+): value is IntervalLabelTokenValue => {
+  return ["Warmup", "Rest", "Interval", "Cooldown"].includes(value);
+};
+export const isLabelTokenValue = (value: string): value is LabelTokenValue => {
+  return isHeaderLabelTokenValue(value) || isIntervalLabelTokenValue(value);
+};
+
 export type LabelToken = {
   type: "label";
   value: LabelTokenValue;
@@ -53,15 +66,15 @@ const tokenizeValueParam = (text: string): Token => {
 
 const tokenizeParams = (type: LabelTokenValue, text: string): Token[] => {
   switch (type) {
-    case LabelTokenValue.Name:
-    case LabelTokenValue.Author:
-    case LabelTokenValue.Description: {
+    case "Name":
+    case "Author":
+    case "Description": {
       return [{ type: "text", value: text }];
     }
-    case LabelTokenValue.Warmup:
-    case LabelTokenValue.Rest:
-    case LabelTokenValue.Interval:
-    case LabelTokenValue.Cooldown:
+    case "Warmup":
+    case "Rest":
+    case "Interval":
+    case "Cooldown":
       return text.split(" ").map(tokenizeValueParam);
   }
 };
@@ -71,7 +84,7 @@ const tokenizeRule = (line: string): Token[] => {
   if (!matches) {
     return [{ type: "text", value: line.trim() }];
   }
-  if (!Object.keys(LabelTokenValue).includes(matches[1])) {
+  if (!isLabelTokenValue(matches[1])) {
     return [{ type: "text", value: line.trim() }];
   }