Exercise capacity has been impaired in the heat as reported by many studies previously (Nadel, 1980; Galloway & Maughan, 1997; Chen et al., 2004). This condition could be due to increased core temperature, dehydration, and muscle glycogen depletion (Carter, 2003). Thus, ergogenic aids have been recommended to cope with these problems.

Ergogenic aids are substances or devices that can enhance energy production, use or recovery and provide athletes with a competitive advantage (Ahrendt, 2001). They are also known as external influences that can positively affect physical or mental performance especially by eliminating fatigue symptoms. To date, herbs or plant products that have been investigated as nutritional ergogenic aids for enhancing endurance capacity are caffeine, ginseng, mahuang, ephedrine and related alkaloids (Bucci, 2000). Eurycoma longifolia Jack is one of the most popular herbs found in Malaysia. It is commonly known as ‘Tongkat Ali’in Malaysia and as ‘Pasak Bumi’in Indonesia. It is also referred to as ‘Malaysian ginseng’since it is well-known among various ethnic groups in Malaysia for treating various diseases and enhancing health (Jagananth and Ng, 2000). E. longifolia Jack is a tall, single-stemmed, slender, shrubby, and slow growing tree, and it can be found on the sandy soil (Ang et al., 2002; Husen et al., 2004). It belongs to the Simaroubaceae family and grows wildly in South-east Asian countries, ie Malaysia, Indonesia, Thailand, Myanmar, Laos, and Cambodia (Jagananth & Ng, 2000; Ang et al., 2000; Osman et al., 2003). Its active ingredients called quassinoids (Ang et al., 2002) are concentrated in the tap root and reach its reproductive age after five years or more (Husen et al., 2004). Traditionally, people believe that this herb can be used as an anticoagulant for complications during childbirth, treatment for dysentery (Osman et al., 2003), aphrodisiac (Ang & Sim, 1997; Choudhary & Rahman, 1997; Ang & Sim, 1998a; Ang & Sim, 1998b; Ang et al., 2000; Ang & Cheang, 2001; Ang & Ngai, 2001; Ang et al., 2001; Ang & Lee, 2002a; Ang & Lee, 2002b; Ang et al., 2003a; Ang et al., 2003b; Ang et al., 2004), antimalarial (Chan et al., 1986; Chan et al., 1989; Kardono, 1991; Ang et al., 1995), antibacterial (Farouk & Benafri, 2007), anticancer (Tee et al., 2007), antihyperglycemic (Husen et al., 2004), anxiolytic (antianxiety)(Ang & Cheang, 1999), diarrhea, fever, hypertension, relief of pain in the bone, and its pounded bark has been used to treat wounds, syphilitic sores, and headache