My HMB arrived yesterday so I celebrated with a pre-ride shake with 10g creatine and 3g of HMB. Followed by a 40mile ride. My plan is to do this daily over the next few weeks when I do my first 100km ride.
My goal is to improve my recovery times. Did some more research as follows (https://www.ncbi.nlm.nih.gov/pmc/art...Fkg%20of%20LBM).

The efficacy of HMB has also been replicated in measures of performance in experienced endurance athletes. Vukovich and Geri [42] investigated the effects of HMB supplementation on peak oxygen consumption (VO2 peak) and the onset of blood lactate accumulation (OBLA) in eight endurance-trained master-level competitive cyclists, with an average training volume of 300 miles per week. Participants performed a graded cycle ergometer test until exhaustion. All participants performed 3, 2-week supplementation protocols consisting of either 3 grams of HMB, leucine, or a placebo daily, while continuing their normal training volume. Results from the graded exercise test indicated that HMB increased the time to reach VO2 peak (8%), while leucine and the placebo did not. The VO2 at 2 mM of lactate (OBLA) increased with HMB (9.1%) and leucine (2.1%), but not with the placebo. Likewise, Vukovich and Adams [43] found that 2 weeks of HMB supplementation in experienced cyclists increased both VO2 peak and the time to reach VO2 peak, while supplementation with leucine or a placebo did not change these measurements.

Knitter et al. [17] examined the effects of 3 grams of HMB or a placebo on muscle damage during a 20 km run in 16 experienced male and female long distance runners. Results showed a decrease in LDH and CK levels with the HMB supplemented participants compared to the non-supplemented participants. These results agreed with Byrd et al. [44] who found that HMB or HMB combined with creatine equally decreased the rise in muscle soreness following a 30 minute downhill run in 28 young, active males; while the creatine only and placebo group did not.

The efficacy of HMB supplementation in the elderly
Several studies have examined if the ergogenic benefits of HMB supplementation can be generalized to the elderly. Vukovich et al. [29] showed that HMB supplementation in 31 untrained, elderly men and women during an 8 week resistance training program resulted in increased body fat lost (-.66 vs. -.03 %), and greater upper (13% vs. 11%) and lower body strength (13 % vs. 7 %) in the HMB condition than the placebo.

Some authors have recommended that HMB should be standardized according to body weight. Using this framework, it is advised to have 38 mg/kg of body weight per day (equivalent to 17.3 mg/lb of body weight per day) [19].

In summary, when supplementing with HMB, current evidence suggests that 1 gram of HMB should be consumed 3 times per day, for a total of 3 g of HMB daily (or 38 mg/kg of LBM).