There are two big categories of aerobic (endurance) sports; weight dependent and weight independent.
NOTE: Now by “weight”, we are talking lean body mass mostly, not lean mass + fat mass. So assume for argument’s sake all the examples below are for athletes with a similar % body fat.
In weight dependent sports how much you weight directly influences your ability to perform aerobically. In these activities aerobic power is measured in millilitres of O2 consumed per kilogram (of total body weight) per minute. Values for sedentary individuals are in the 25-35 ml/kg/min range, genetic freaks in the elite sports world can exceed 100 ml/kg/min.
Sports in this category include running, cycling, rock climbing, etc.
Weight independent sports are those where how much you weigh has little to no influence on how well you can perform aerobically. Aerobic power values for sedentary individual are in the 1.75-2.0 l/min, and elite athletes can exceed 6-7 l/min.
Sports in this category include swimming, paddling, rowing, etc.
Aerobic power is specific to the sport you are doing, so should be estimated on a paddling erg for paddlers, treadmill for runners, rowing erg for rowers, etc.
Now as with everything in life, there is no black and white delineation between weight dependent and independent. There is a spectrum. Even within a given sport there is variation. In cycling, bigger heavier riders are favoured on the flats, smaller lighter riders on the hills. XC skiing is the same, flats and downhills favour bigger skiers, and steep uphills favour lighter skiers.
In those sports where weight is both an advantage and a disadvantage, aerobic power is then expressed neither as weight dependent or independent, but a little of each as a function of the sport’s requirements. Leaving the math aside, sports scientists look at the characteristics of the top performers in the event overall, and then express the aerobic power as a function of body mass to a certain mathematical power (where kg^0=1 or weight independent, through kg^1 weight dependent);
So now we have ml/(kg^0)/min (which is equal to l/min) through ml/kg/min along with the in between values, i.e. xc skiing overall is ml/(kg^2/3)/min while on the flats it is l/min and steep uphills it is ml/(kg^2)/min.
Ocean paddling is relatively devoid of sport science research, but flatwater canoe and kayak often express aerobic power as weight independent, so lean body mass has little effect on performance. The physics of hydrodynamics tends to confirm this with little additional drag due to increased body weight in a given hull.
However, in open ocean paddling we often have up and down sections. Without fully understanding all the relationships and intricacies involved, we would probably be safe saying surfski is weight independent on flats and as it gets rougher, a small weight dependent factor creeps in.
To counter that, surfing is also much more of an anaerobic activity where strength and power are advantageous in catching waves. Increased anaerobic power is often associated with increased muscle mass, so we may well see that weight dependent performance factor nullified by this need.
So all in all, being heavier (lean body mass) is an advantage if that muscle is trained to paddle. Some of that muscle will contribute to performance from aerobic fitness, some from anaerobic fitness.
However, technique, open ocean skills and wise preparation are often the deciding factor
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