Background: Power is reduced in people with Parkinson's disease as a consequence of bradykinesia, but it is not clear whether reduced power is also due to a deficit in force production. The aim of this study was to quantify force production in all major lower limb muscle groups in people with PD during the “on” phase after medication, compared with aged-matched neurologically normal control participants. Method: Design: A cross-sectional study was undertaken. Participants: Thirty ambulatory people with PD and 24 neurologically normal controls. Outcome measures: Isometric force production of the hip flexors and extensors, hip adductors and abductors, hip internal rotators and external rotators, knee flexors and extensors, ankle dorsiflexors and plantarflexors, ankle invertors and evertors using hand-held dynamometry. Results: There was a significant deficit in force production in participants with PD in all lower limb muscle groups tested, compared with control participants. On average, force production of participants with PD was 78% (range 67%–87%) of control participants, despite participants with PD regularly participating in exercise, being measured during their “on” phase after medication and having normal walking ability. The most severely affected muscle groups were the hip adductors (67%) and ankle plantarflexors (68%). Conclusion: People with PD have a significant loss of force production in all lower limb muscle groups compared with age-matched neurologically-normal controls. Implications for Physiotherapy Practice: Clinicians should regularly assess the strength of all lower limb muscle groups, regardless of participation in physical activity, responsiveness to levodopa medication and walking ability.