Array of inputs Angular 7

Rafael, think in FormArray

First create a function that return a formGroup, and a variable that was a FormArray

formArray:FormArray;

createGroup(data:any)
{
   data=data || {serie:0,repetition:0,weigth:0}
   return new FormGroup({
       serie:new FormControl(data.serie),
       repetition:new FormControl(data.repetition),
       weigth:new FormControl(data.weigth),
   }))
}

second in a ngOnInit create the formArray using your array exercises. You can loop over exercises and use push or use map

ngOnInit()
{
    this.formArray=new FormArray(this.exercises.map(x=>{
        return this.createGroup(null)
    })
}

You simple iterate over FormArray.controls.(*)

<form *ngIf="formArray" [formGroup]="formArray" (submit)="submit(formArray)">
    <div *ngFor="let group of formArray.controls;let i=index" [formGroup]="group">
        {{exercises[i]}}
        <input formControlName="serie">
        <input formControlName="repetition">
        <input formControlName="weigth">
    </div>
    <button type="submit">submit</button>
</form>

You can see the code in stackblitz

(*)Yes, there're severals ways to iterate over a FormArray. The clasic is a FormArray in a FormGroup and we use

<form [formGroup]="formGroup">
  <div formArrayName="formArray">
      <div *ngFor="let group of formGroup.get('formArray').controls; let i = index;"
           [formGroupName]="i">
           <input formControlName="...">
           <input formControlName="...">
             ...
      </div>
  </div>
</form>

But if we has only a formArray, we can simply loop over formArray.controls and indicate that the [formGroup] is the variable over we iterate. We are replacing [formGroupName]="i" by [formGroup]="group"