Abstract Background Hip fractures represent a global public health issue that demands high cost both from the patient and from the society. Functional exercise in the subacute phase of a hip fracture is essential in reducing these costs. To the best of our knowledge, no qualitative study has explored the patients’ experiences in participating in an exercise program during the first month after surgery. Thus, this study aims to explore how older people who had participated in an evidence-based exercise intervention describe their relationship with their therapists and how this relationship might contribute to their motivation for exercise. Methods Thirteen women and six men, who all had experienced a hip fracture and were staying in the same short-term rehabilitation unit, were interviewed by the last author. The interviews lasted from 30 to 70 min. The participants’ mean age was 86 years and they had all participated in a High Intensity Functional Exercise (HIFE) program in one-on-one sessions for 2 weeks, a total of 10 sessions. The recruitment was done by therapists involved in an RCT evaluating the HIFE-program with the attempt to obtain maximum variation. Data were analyzed through systematic text condensation in collaboration between all authors. Results The analysis yielded three main themes integrated in the core theme “Therapeutic alliance is an interpretative filter for the participants’ experiences.” The three themes were “The feeling of mutuality and respect in the alliance”; “A trusting and motivating relationship” and “Tailoring of the instruction and program to make the task understandable”. These themes concerned basic needs in the relationship between the participants and the therapists which brought forward a feeling of mutual respect. The most prominent finding was the experience of trust in the therapists’ abilities, and how this contributed to the participants’ motivation to fulfil the program and achieve meaningful changes. Conclusion Our findings suggest that therapeutic alliance is an indispensable aspect of a therapy, and relational knowledge and competence are prerequisites in the transfer of professional knowledge in a therapy. Our findings can be useful to therapists involved in clinical practice, especially to those working with vulnerable groups.