Although the stress is on swimming and sailing, you may well prefer to do nothing more strenuous than lie in the sun and be a spectator.
Swimming is compulsory and no-one is allowed to spectate.
mnli hypothesis: Swimming is compulsory and no-one is allowed to spectate. premise: Although the stress is on swimming and sailing, you may well prefer to do nothing more strenuous than lie in the sun and be a spectator.