Carstensen was under contract with Dortmund, who will also be participating in the Club World Cup, until June 30, 2025. However, sporting director Max Eberl acquired his services just in time for the Club World Cup. Eberl knows the nutritionist from their time together at Borussia Monchengladbach.
At Gladbach, he earned the nickname 'Miraculix' — a nod to the wise druid from the Asterix & Obelix comics who concocts the magical potion that gives the Gauls their superhuman strength. Much like his cartoon counterpart, Carstensen believes in the power of the right formula. After training sessions, he turns to specially prepared recovery shakes, rich in carbohydrates and protein, to quickly replenish energy and support muscle repair.